Lots of reasons for high stated prices at gun shows:
1. A good vendor is good at "jawing" with anyone who passes their table. (Why do you think the beef jerky guy and the knife sharpener keep coming back). They'll get someone talking about Obama, gun bans, some conspiracy theory, etc. If the vendor can get the looky-lew interested in something, he can always make him the "deal of a lifetime".
2. Vendors are not usually looking to sell to folks who are extremely knowledgeable about firearms. They are looking to pluck cash from idiots - and there are plenty of them out there.
3. Vendors also like people who have too much money they don't know the difference any longer between $1,000 and $50,000 - these are the vendors selling "collectors pieces".
4. Some vendors use shiny Pythons, Colt SAA 1st gens, or Class III stuff to attract folks to their tables - they aren't necessarily looking to off-load their really good stuff, unless someone really, really wants it.
5. There are a few folks who just like their junk more than they like money - maybe buy/sell guns more as a hobby.
6. Last, but not least, some buyers don't realize that the market value of many guns has gone up - they may think prices are out of line when (sometimes) they really aren't.