Back when we had a claw machine with plush toys in nearly every grocery store, it was generally a well-known fact that it's a game of chance much more than it is a game of skill. When it didn't want you to win, it just didn't grip as hard as would be necessary to hold the toy. It would either not grab it at all, or it would but then would drop it due to an abrupt stop when it hits the top while lifting the claw.