I want to buy new speakers for 50,000 and see it used for 30,000, what should I do?

Assuming both have return privilege, buy both at the same time.  Audition them in your home side by side.  If you can't hear any difference, return the new pair.  If you hear anything bad from the used pair that you don't hear from the new, return the used pair.

This should result in COMPLETE confidence that you made the appropriate decision. 

I guess the overriding concern that I have is that I think everyone knows speakers can be very overpriced and that’s really absurd.

Manufacturers create subpar speakers at lower price levels and tempt you to buy higher priced speakers that sound better. It’s a con game. They are taking advantage of the seductive nature of listening to things that sound really good to us. It’s affecting the part of the brain that lacks the good judgment when it comes to spending money.

Think about it, why are we being encouraged to spend $50,000 for the type of speakers we all should be listening to

Get the flagship product of a brand that typically produces affordable product. A lot of aptitude, care and devotion will typically go into such a product.

You get the bottom end (deliberately gimped end) of a thieving brand and what you’ve mentioned could be true. There are some exceptions where good things can trickle down, but, that’s relatively rare.

Are the $30K used speakers in the condition you would want? For that money, I would travel to see them and listen to them. If they were what I wanted and were in acceptable condition, I would buy used. The value, assuming they still worked should be more stable and less likely to depreciate as significantly as from new once already "used." What matters is whether the speakers still have manufacturer's support or absent that, whether key parts can still be sourced. I have bought new and used, and usually prefer the latter for the money savings. $20K is nothing to sneeze at, or at least it shouldn't be, and there are many things one could do with those funds. As for projecting how long you would keep them and rationalizing the new vs used costs, buying used affords you the option of selling them off with less loss if you should change your mind about them. IMO this same rationalization applies to many purchases.

@chenry 

I really don't think the 30K or the 50K speakers exist.

The business of new vs used is difficult. 2 yrs in a speaker life is NOTHING.

Speakers sound better with use. Short of abuse, no worries. 

But i would insist on hearing them in person, inspect for physical damage, make sure the mfr crates are in PERFECT condition, and either transport them myself if practical or ship with insurance. 

1st flip on most anything in a 3rd party sale is 50% off plus maybe a little wiggle room. Is the MSRP 50K? Is the person the original owner? Warranty transferrable? Original purchase receipt available? 

Do your diligence on such a large purchase. Nothing sells for the full MSRP these days, and if you bite, your problem becomes his ex problem.