How to choose a cartridge you can't hear on your system?

inna, i'm not sure as to who you are responding to. However, your thought that by waiting a dealer is going to be essentially begging you to buy, just doesn't seem to jive with reality. 
IME, the dealers are all pretty independent when it comes to this issue. While i agree with you that this is not in the best interest of the consumer, it certainly seems to be a somewhat uniform response....at least in the dealers in my area. In some ways, i cannot blame them, once a cartridge is mounted it becomes a 'used' device. How the mounting and care of the cartridge is accomplished is also a variable. When we are talking of multi thousand $$ pieces, the rest follows along. Not at all a great situation for the consumer, and certainly one that I would love to see changed, but I see both sides of the picture. 
Buying without listening first is, at least IMHO, never a good thing to do....unfortunately,with cartridges, I don't see a lot of options! YMMV.

@daveyf at the same time there are many people who can buy demo from the dealer with warranty to save 30-40% at least on multi thousand $$ cartridge, most likely you're talking about MC cart only. Demo unitls sells well, in fact i bought demo amp, demo speakers, demo tonearm and happy about them, no issues. So for the serious dealer it's not a problem to have demo and to get rid of demos. But this is a proper customer service. I think the dealer must have a demo set-up with demo units, the re-seller or shop may not have demos. 

Great question...the answer is you can't.  The dearth of stores willing to demo cartridges are dwindling, and even if you hear two different cartridges in the store, setup is oh so important (I look askance at all "experts").

Dealers could have at least a few set-ups for auditioning.
Not my problem, though. When and if I am ready to pay thousands  of dollars for a cartridge, I'll make couple of phone calls and get precise advice. You got to have priviledges and connections, then you'll be fine, cartridges or not.

Let me ask a different question.  Can one generalize that a high end cartridge of a manufacturer produce system synergy if their lower end model(s) do?  

I'm curious if it is always a crap shoot or if one could try several "cheaper" models and then commit to their flagship with success.