we don't necessarily see the examples where it doesn't work well.

Actually, his TV show included some outtakes of some of his attempts at things not working well: paying with fake money, robbing a person by handing them things and then having them hand back more things than he originally gave him, etc. It appeared as though the purpose of including these segments was to show that the tricks he was using didn't work on everybody in every situation.

Of course, that could just be what he wants us to think... ;-)