One of a pair of con artists, posing as a retired violinist, leaves his precious violin as collateral against some small debt while he goes and fetches the cash. While he's gone, the other con man presents himself to the mark as an instrument dealer — business card and everything. He wants to have a look at the violin he saw in passing, and as soon as it's produced, he's delighted — as he thought, it's an original Stradivarius! It's worth hundreds of thousands of dollars! He must have it, but he has a plane to catch and can't wait for the old man to return — Dear sir, would you please give him my business card?
Now the mark's greed comes in. If he's a good man, he gives the old violinist his instrument and informs him of his good fortune, and the scam has failed (the cons have lost nothing, however). If he's a lowlife, however, the scam may succeed. He offers the old man a thousand dollars for his violin — the old man clearly has no idea of its actual value, but loves it like a family member. The price goes up and up, and eventually the con artist gives in, selling his beloved violin for ten thousand dollars. He walks out with the money, and the new owner waits a bit, then calls the number on the card. It's a false number, of course, and any professional will immediately recognize that the violin is worth perhaps fifty dollars, and the old man and the "dealer" meet up to split the take and get another cheap violin.