My brother-in-law lost his wallet at the Elizabeth Park Marina.  A day later, a female called him and said she and her boyfriend found it.  He was relieved and asked where he could meet them.  She then went on to say they wouldn't be returning it unless there was a significant reward paid at the time of the exchange.  Of course, his initial reaction was an angry outburst but after a minute or so, an idea popped into his head.  He told them that he would give them what they wanted - that he just wanted his wallet and contents returned.  

This story is second hand but as I recall, he told her he would call her back in a day or so after he got back in town (he said he was about to leave on a short, work-related trip) and had the chance to stop by the bank to withdrawal the required funds.  She & her dirtbag boyfriend were satisfied with that arrangement.

He called the police, told them the deal, had an officer (or detective) listen in on the return call, duped her into repeating the demands, and went to meet them.  The police were waiting, saw the money and wallet change hands, and arrested the two criminals.

Since this was told to me and not witnessed, my recount of the details may not be 100% accurate but as far as I know, that's how it all went down.  He got his wallet back and they went to jail.