My games get roughed up more in a single league night than they do in 500 plays at a show.
Only twice have I seen something truly abusive at a show: someone lifting up a machine and dropping it to free a stuck ball (as the OP described). I immediately jump in and yell "hey, hey, hey - that's really bad for the machine. What's the problem where? Hang on, I'll get the owner".
The type of person who wants to slam a machine like that is not the type of person who wants to wait around for a resolution to the problem, so he will wander off. Obviously the person has done it before, and thinks he's being helpful. So try and butt in with a very scolding tone.