How many hours on a engine before you should shy away from a deal? I know it depends on many things , but in general with average maintenance. I know an auto block runs thousands of hours .

I'd shy away from too low as much as too high. Generally in the midwest people put around 50 hours or so on a boat per year, but that would not make me shy away from one with upwards of 100 hours per year if I knew it was taken care of properly.

Your question is a tough one - since proper maintenance cycles and good oil is way more important than pure hours.