A person comes up to you claiming to have found a gold ring and asking if it's yours. When you say no, they show you that it is much too big for them and offer it to you anyway, as it's no use to them.

You either worry about the person who *did* lose the ring and suggest returning it to the police station or take the offered ring. If you take it, the scammer asks for a few euros for "good luck" or whatever, as after all he did find it. I took it, but told the scammer I'd take it to the police station and hand it in, at which point he took it back, telling me he'd do that himself :-)