What should I do?

Recently, at a brick and mortar audio dealer, I listened to a high-end moving coil cartridge.  It sounded really good, and I was impressed.  The retail for this cartridge was more then I wanted to spend ($4500), but to make a long story short, the dealer offered me a rare deal, ($2500+tax) brand new, so I bought it.  Got it home, and carefully installed it last night.  I listened to it for about 2.5 hours.  It is really good, but I don't think (at this point), that it's that much better then my old cartridge (at least, not yet).
Ok, so this morning I played around with the loading.  Better, but still I'm not happy.  Now, with only about 5 hours on this new Cartridge, I realize that it's not broken in yet.  I'm looking for input as to your thoughts on how I should proceed.
1.  Are cartridges purchased from high-end dealers returnable (I don't want to create any bad feelings with this dealer, since he gave me such a good price)?
2.  I was told 50 hours of break-in time for this Cartridge.  Should I wait the break-in period to make any decisions?
Any thoughts on how you think I should proceed are appreciated! 

Are cartridges purchased from high-end dealers returnable ...
That was an option with some dealers, once upon a time, but I’m not aware of any dealer who would offer such assurance today.

It might be helpful for you to identify this mystery "high-end moving coil cartridge."
The hardest thing for me to break in are cartridges, I have a few moderate priced carts that will and did sound better than my top tier carts until they were broken in, for me it's just a grueling process. That kind of price break from a dealer is probably just a sign of the Times and sounds like a really good deal. Enjoy the music
You cant judge the cartridge until is actually past break in. You need to experiment with loading as the proper setting can sometimes be surprising and not what is suggested by specs. You also need to have a system of sufficient quality to appreciate the more sublime aspects of a better cartridge. Details about your entire system would also be helpful.

Something to keep in mind is the conditioning of your tonearm cable. We just bought a Audio Kharma conditioner and the most profound improvement we have ever heard was the conditioning of this wire. 
If it doesn't sound good right out of the box odds are it never will. That goes for everything. Even cartridges. You should be loving it from the first side. Then loving it even more after you've got it nicely dialed in with VTA and loading. Then from that point on there should be anywhere from a few weeks to a few months of one night after another being surprised at catching yourself enjoying aspects of music you never noticed before.

That's what it should be like. Unless you are prone to buyers remorse. Which tends to be more likely on impulse purchases. Which between the way you said zero about doing any research, or even that you were looking for a cartridge, and seemed to have bought based on price without even asking about terms, sounds like an impulse purchase to me. 

Don't really know what you should do. What I would do is pay more attention and consider a little more carefully next time.
First you need to share a few things:
1. What cartridge are we talking about?
2. What system did you hear it with at the shop?
3. What system do you use at home?

The dealer should obviously have told you this, but the sound of a cartridge is system dependent. This might go a long way to explain why you were impressed at the shop and less so in your own home.   

There are exceptions, but it's highly unlikely that the dealer will accept a return and offer a full refund. Not immediately and certainly not after another 50 hours of break-in. If you stay underwhelmed, you might consider asking the dealer to come over and check if you installed it correctly. 

 It sounded really good, and I was impressed.  

 Got it home, and carefully installed it last night.  I listened to it for about 2.5 hours.  It is really good, but I don't think (at this point), that it's that much better then my old cartridge (at least, not yet).    

Then why did you buy it ? Hypnosis ? 

Some of the reasons it did work in your room:
-The dealer system was completely different than yours ? 
-You don't have an appropriate tonearm or phono stage ? 

Personally i don't believe in warm up process, if your cartridge is brand new the things getting better in first 50 hrs, but not so much. 

Maybe you just don't like the character of this cartridge in your system, especially if it does not sound better than your old cartridge.

If it's not better than save $2500+ 

Return it, explain your opinion to the dealer, ask for another cartridge (ask for something to match to your tonearm and your phono stage).

Or bring your old cartridge to the dealer and compare them.  

Or just get full refund and forget about it.  
Sounds like a super deal without a return. You should have initially inquired before buying.
I'm surprised the dealer was demoing a cartridge that wasn't fully broken in.
Without the information that others have requested, like what cartridge it is, it's hard to judge your situation.
Cartridges are like ski boots. Once you use em you own em. Unless it is a demo unit it will not be returnable. Whether or not it sounds better in a few hours depends. I have a Clearaudio cartridge that out of the box was very bright. I had to program a special curve for it. But it tracked wonderfully and had great separation. Eventually it started sounding dull. I set the curve back to flat, perfect. I can't tell you how many hours it took. I would say a month of steady listening.
Most important is set up. Unless you are using a test record it is unlikely that you are getting it optimal. I recommend the HiFi News Test record. Get your anti skate set right and your resonance frequency down around 8-10 Hz and I promise it will sound better. 
You got a great deal so it is unlikely that you will find a $2500.00 cartridge that is better. I do not know of any bad $4500 cartridges although you will never see me buying a Decca. 
I’m guessing the dealer was using different components than what you run at home but did you ask what gain and loading settings he was using? If the cart doesn’t sound nearly as good as at the dealer I suspect it was one or combo of:

1. The components (primarily table/arm/phono pre/SUT) were a better match than yours;
2. You don’t have gain and loading dialed in optimally;
3. The cart isn’t set up ideally in terms of overhang, VTA, VTF, etc.

you will never get agreement here about break-in, but exact setup is crucial...but since they say 50 hours and it's Saturday afternoon, play a lot of records and give the dealer a call...

Take it back to dealer and have them reinstall in the original rig. If it sounds great again, you'll know your system is the problem.
And bring your own old cartridge to the dealer to compare it with new one.

If you're not happy with the sound and can't solve the issue at home what is the reason to pay $2500 for this new toy? 
And don't forget to tip the dealer (offer, at least) as mounting cartridges as a PITA.
If @louisl doesn't respond with the info requested this is a complete waste of time.
All very helpful suggestions here weighing the available options. "If @louis doesn't respond".., we know where he should put it! 👍 HA
No dealer will take a cartridge back unless it is broke,check VTA it will have to change after cartridge is broken in.What is the name of this mystery cartridge.
What is the name of this mystery cartridge.

Ha...i was wondering the same. I may offer to buy it depending on what it is assuming @louis decides he’s done with it. ;-)
Dear @louisl : All LOMC cartridges when we buy it in new condition always needs that the cartridge suspension settle down before we can " play " with loading and other cartridge/tonearm set up parameters.

You need to start with the cartridge manufacturer recomendations/specs and after the set up been that way just let play the cartridge for at least 50 hours with out putting to much attention to its quality level performance, you can't have under scrutiny or make any changes in its set up.

Then after those 50+ hours you will re-check the overall cartridge/tonearm set up: overhang/overall geometry alignment, VTF, VTA/SRA, azymuth, antiskate, changes on loading and the like.

That means that now you will start the cartridge fine tunning till you find out that the qualioty performance of that cartridge is " there " where you really like it.

I know you own/owned SS cartridge, Lyra Kleos and an old very good 0.2mv LOMC cartridge ( that I owned but I can't remember the manufactuerr. ) and that use/used VPI tonearm that I don't like it not only with LOMC cartridges that are more demanding than MM/MI ones about tonearms especially with unipivots like your VPI.

In the other side iof your new cartridge is really a top tier and you are using tubes then there is an additional problem.

Do what you want it because you never give answers to what other gentlemans ask for when you are the OP   ! ! ? ? ? whom ask for advices. LOL.

Regards and enjoy the MUSIC NOT DISTORTIONS,
That could certainly be the problem. If you have A VPI unipivot or any unipivot tonearm including the Graham get rid of it. I know of no LOMC cartridge that would be happy in a unipivot arm, way to floppy. The Graham is the best of them being stabilized with magnets but there is no reason to resort to that type of maneuver when for that kind of money you can buy the best bearings made. A tonearm can move in only 4 directions, up + down, side to side. In every other direction it has to be rock solid. This is particularly true with today's low compliance cartridges.
This is way more important than any reduction in friction, if any a unipivot might have. The forces involved playing a record are more than enough to overcome the friction of even the cheapest tonearm bearings out there. If you don't believe me defeat your antiskating and put your arm down on a blank disc and see what happens. Better have your catchers mitt on. It is actually more important that a bearing be smooth rather than the lowest friction. A tonearm can not make a cartridge sound better, but it can sure as h-ll make them sound worse, a lot worse. Way back I know a guy who mounted a Koetsu in a Transcriptor's Vestigial arm. The poor Koetsu would jump out of the groove. Forget about sounding bad. It was totally unplayable. Anyway when you put a LOMC cartridge in a unipivot arm what you usually get is muddy bass and dull transients even if the effective mass and compliance match up. If you really have to use a unipivot arm go find yourself an old Shure V15. If the arm is too massive just drill a bunch of holes in the arm tube.

Sorry guys that I haven't responded, but I am trying to put some more hours on the cartridge for break-in.  
To answer everyone's question about this "mystery" Cartridge, it is a Mytech Hyabusa mounted on a VPI Classic 3 (JMW Memorial 10.5 unipivot tone arm) feeding a PASS XP-17 phono preamp, High Fidelity cabling.
I now have a little over 8 hours of play time on the cartridge, and it is really starting to sound very good.
First, I appreciate everyone's input, but I find one comment that is if don't respond, then "he knows where he could put it" a bit condescending, unnecessary, and not helpful.   
Cartridge break-in is a slow process, that takes time, so please understand that is what I am doing.
I will respond again, after I our another 10 hours on the cartridge, to keep everyone updated.  Again, thanks to everyone for your thoughts, and suggestions.  I appreciate it!
Nice, don't forget to put your old cartridge back for final comparison to that new one after break-in.

We're always biased by new toys, the trick is to make a fair comparison after all, would be interesting to read. 

I think this happens to a lot of us: we make a big outlay and there aren't immediate results and then the remorse/concern comes. Two things happen (to me, at least): First, things take time to break in when you are at the level of your equipment. Definitely. But also, when you get something new, often it has a different presentation than you are used to and it takes time to adjust to that. Unless it's truly horrible sounding, I try to give everything a couple weeks of regular listening before making a decision. 
You are absolutely correct!!!  I'm such an 'Immediate gratification' kind of guy, that when I installed the cartridge, brand new, cold, out of the box, I wanted it to blow me away....immediately.  Well, that just didn't happen.  I really need to learn to have a little patience.
The Mutech now has 12 hours of play time, and it is really beginning to sing for me.  I've never experienced such a transformation in a product during the break in process, as I am experiencing now with this Mutech.  

i hate installing cartridges.  A lot of time and patience required.  However, in this case, once I have 50 hours on the new Cartridge, and I feel that it actually is broken in, I will put my old Cartridge back, for, as you say, a final comparison.  Good suggestion, thanks!

You have a very good cartridge! We sold one of these to a client and it was the best we had heard at its retail price.

I heard the Mutech not only at my dealer's store, but also in a friends system.  I knew then that it was one of those 'special' cartridges.  However, when I got it home, and installed it, I was much less then impressed.  I should have realized, that with zero hours, it was going to take a little time to wake-up.  Welll it certainly is waking-up, and sounding really very good.  Thanks for your comment!
Our pleasure. Wanted to make certain that you knew our opinion. Our company (2 people) havent heard all of the cartridges in this price range, but your cartridge certainly bested some of the bigger names we auditioned.
Latest update.  
I now have 15 hours on my new Mutech Cartridge.  Two important performance increases have occurred.
One, at, or about 6 hours, the cartridge's bass has matured.  When I first installed the Cartridge, the bass was extended deep, but it sounded as if the bass volume had been turned down.  No longer, it is now both extended, and full.  Rich, and detailed at the same time.  
Secondly, at 15 hours, the stage is opening up, and extending way outside the edges of my speakers.  Depth (on recordings that have depth) is also improving.  Image specificity is precise...voices that are sung together, are heard with distinction.  Each voice being defined, and heard in its own separate space.
This is now turning out to be one great Cartridge.  Real improvement over when I first installed it.  With only 15 of the recommended 50 hours of breakin, I'm hoping to hear even more.  
This is really one hell-of-a-good cartridge.  I will update when I get to the 25 hour mark.  Again, thanks to all for your comments! 👍
20 hours now on the cartridge.  This Mutech Hayabusa is already beyond my expectations.  At this point, I just can't imagine how it could get any better!  I will update again after another 10 hours of play time.  
louis, Sometimes things require a little patience. I'm glad your cartridge is now blossoming and you didn't.... "we know where he can put it", in which I meant, back in the box and on the shelf, of course. Enjoy!
“20 hours now on the cartridge. This Mutech Hayabusa is already beyond my expectations.” 

So where are you now with this cartridge?  What cartridge(s) have you had in the past?  I’m curious about this cart and there’s very little user (or professional) info out there.  Thanks!