I found a $50 bill next to a car parked outside my apartment block a few years back. I immediately suspected a neighbour of mine had dropped it, went to his unit and asked him if he'd lost any money. He puled out his wallet, checked and exclaimed. "Cripes! I've lost $50. I had five now I've got only four."
That's how I knew he was the man who'd lost same because I did not mention an amount. I can tell you he was very relieved.
The result was that we both felt better about that find: I as the giver and he as the receiver. Yet, in reality I gave him nothing. Definitely a win:win.