It seems simple if you weren't raised by savages. Respect other people's stuff.
Pinball machines are built to withstand shaking, within a reasonable range. Nudging is as much a part of the game as outlane drains. Some tables even leave the factory with shaker motors.
Picking up the cabinet and slamming it on the ground is not in that reasonable range. Nor is beating on or kicking the coin box. Those people should be kicked out of and banned from a pinball location, to say nothing of these shows and festivals.
If it wasn't for these heathens, I might actually expect to find some good pins on location, so that it's not like finding the needle in the haystack when you see one on which everything works.