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

This is definitely a personal thing. It depends on your personality.

If it were me, I would be planning on keeping these speakers for ten years or more. I would be incredibly disappointed in spending $30K and getting something scratched or banged up, let alone if there was a sonic problem… I would probably slowly realize. For me $50K is a lot of money. Also, my dealer would give me credit for them if I chose to upgrade in five years. He will come and set them up. But that is me. I want absolutely no uncertainty involved in a large purchase like that. If I bought used and they were all scuffed up… I’d end up selling them and buying new ones. That is me.

Some guys would be proclaiming what a genius they were for getting such a bargain and they would love that every time they sat down and listen to them.

Buy what you want; you are not insane.  New or used is a personal preference.  Do you buy a new car or will you buy a 2 year old one with 20,000 miles for this similar discount?  Most nice equipment is actually cared for extremely well.  Look at the entire system, call the seller.   you can tell.  Probably.  :)

PS I bought my nice speakers as demo's, from a dealer who (like GDP says), installed them and stands by them.  This may be the best of both worlds.  Cigarette smoke smell would be a killer for me.