Re: How many hours?
I've had several marina owners over the years in Ontario cottage-country (May-Oct season, generally speaking) tell me 30 hours a year is about average for a recreational family boat in these waters. I generally do twice that in the same time frame.
A competent marine mechanic could give you a good idea of the condition of the motor but you can also pick up some clues based upon cleanliness of the engine and engine compartment, condition of oil and gearcase lube, condition of outdrive, zincs, skeg, prop, etc.
No iron clad guarantee it's been taken care of as opposed to detailed at the last minute but you can certainly spot neglect if they don't know how or care to hide it.
I think some later model engines might track hours in their engine management systems and available to techs with the right scanning equipment but by far most boats still on the water are too primitive for that I imagine. Good luck with the search!