I have no use for someone that takes advantage of a seller that has no knowledge of what they have or what the market is. On the other hand, if a seller intends to set up at a gun show it is up to them to research what they have in order to protect themselves.
One of the best stories involved three people I knew, and a gas trap M1Rifle. I don't know the first part of the story to be true, but do know the latter part is. Supposedly an elderly gentleman advertised a "Garand" in a local paper but got no serious responses, and this part I can't verify. He then took it to a local gun show priced at $750, and got no takers. Finally someone offered him $500, and the old gentleman took it. The new owner, who I know, then took it to a gun show regular, who I knew, and traded it for a pistol and $500 (see, he got his money back and a free pistol). The new owner had it for approximately a month before he took it to the Houston gun show and put it out for sale at $1250. The first person to see it was Peter Cardone, and ask the price. Mr. Cardone though the seller said the price was $12,500, and was going back to his table to get the money to purchase the rifle. Just before he walked off he ask the seller how much a Civil War carbine was, and was told that it was $1250 also, but he would take $2400 for the pair. It was at this time Mr. Cardone realized the gas trap was not $12,500, but $1250. Mr. Cardone said he was floored, as he thought the $12,500 was an absolute steal. He said it was one of those situations where you carry no responsibility to tell the guy he is selling it too cheap; ask me more for it. Naturally he bought it and immediately priced it at $50,000.
The seller had plenty of time to research what he had, but just didn't take the time. It would have taken no more than five minutes to find out that he had something special, as it is probably the best condition original gas trap out there. It was about as close to new as they get, and totally original.
I got to see the rifle at Tulsa, and ran into the original buyer at $500. He turned rather pale when I told him to go look at the rifle he couldn't wait to get rid of.