A guy discovers a wallet with $700. A few days later, he comes across a note informing him that a rich man lost his wallet and that anybody who finds it would get a $50 prize. 

When he eventually finds the owner and hands him the wallet, the wealthy man tells him, I see you have already taken your reward, after counting the cash.

What are you talking about? asks the poor guy in response. This wallet had $750 in it when I lost it,  the wealthy man says. After some argumentation, the two men decide to resolve their disputes in court.

The poor guy makes his case first, followed by the wealthy man, who ends by adding, Your Honor, I trust you, you trust me.

The judge responds, Obviously. The poor guy is horrified while the wealthy man grins. The Judge then delivers the wallet to the poor guy who discovered it, taking it from the affluent man’s hands. 

Angrily, the wealthy man shouts, What are you doing? In response, the judge states, You are, of course, an honest guy, and if you claim that your lost wallet had $750 in it, I’m sure it did — but this wallet must belong to someone else because if the man who found it is a liar and a thief, he wouldn’t have returned it at all. The money belongs to the person who found it, unless he comes forward to claim it. «How about my money? asks the wealthy man. We’ll simply have to wait till your wallet with the $750 is found.»