Card shows are filled with people who conduct cash transactions with no receipts. Taking off my rose-colored glasses for a moment, I wonder what would stop a pair of con men from committing fraud this way:
- Criminal #1 sets up a table at the show
- Criminal #2 "steals" a high-dollar card from that table
- Criminal #2 sells the high-dollar card to a legit dealer
- Criminal #1 "discovers" the card and claims they are the rightful owner of stolen property
- The criminals now have the card back and the money paid by the dealer
Personally, I'd call the police, the show promoter, and a lawyer...and not necessarily in that order.