On my Cheetah, when I got it, someone drilled a hole and put a flipper button on the upper left of the front of the cabinet to add credits. The problem is that is where 80% of games have the start button.
Took the game to a show and every time I went to check on it, the game was off. I was watching and people would come up to the game and try to start it but they were actually adding credits, when the game wouldn't start they'd shut it off. Obviously these people didn't know about the start button on the coin door.
Took the game home, removed the button and filled in the hole. I've added a small credit button behind the coin door to add credits. Now it's less confusing for people.