Interesting topic. I will get to a point where I feel like the machine is telling me I'm done. When I can't score specific shots, can't clear 100k, cant get a single special shot or multiplier. When I get to that point, I just figure it's bedtime or quittin' time. When a machine (or machines) shut me down consistently I take it as a sign. Go to bed, man.
This might be different in an arcade? In an arcade, I move on to the next pin of interest in the lineup. If they all shut me down or I cannot find my shots, thenit is time for a beer and maybe an arcade game or two. Still can't feel good on a game, that's my sign. Game over, man!