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

Would you be buying the used speakers from a dealer? If yes, do they offer any kind of guarantee or have a return policy?

If they are newer speakers, replacement drivers are probably available, but I'd check.  I'd be concerned about buying an old set of speakers.  Drivers go bad with age and replacements might not be available.

I've never bought used speakers, but for $20k, I would consider it if they check out. They may have been owned by someone like me. The used stuff that I've sold was in like new condition. 

I have owned many speakers that msrp’d in the higher end brackets, never lost anything when I rotated them out. I buy such items used, etc or negotiate some cut even price with some dealer/others (helps if you know people). If you are not sure you will hang onto something for life/a long time, try and buy at a ’cut even’ price.

I would suspect 50K speakers haven't had a very hard life. There are very few 50K party speakers.  The other option is to find a used pair of even better speakers for 50K.  You would be less likely to want to exchange them in the future.

$50k buys you a lot of speaker new or used. Call Mike Powell @11stereo.com. His F&F lineup is very good and he always has high end used gear for sale. I have made several purchases from him and he is good people.

@OP - your post does not raise a concern that very nice speakers are too expensive. With very rare exceptions, consumer goods depreciate. Not nice speakers depreciate and very nice speakers depreciate. Actually, very nice speakers depreciate less.  Speakers have a long service life so their depreciation can be amortised over many years. Anyway, that has to be set against the pleasure of listening them, and what price does one put on that.