If there is a forum for the brand of boat you're looking at, I'd get on there and see what you can find. In my experience, lots of stuff is brand-specific. E.g. did the manufacturer use any wood on the boats; where are the usual trouble spots and how to fix. Some general stuff:
Engine hours, check the oil level and color, note the engine make and model and research longevity/issues/winterization/maintenance proceedures online, Have the gauges been replaced (might not have set the engine hour meter to actual hours when replaced), does it go in and our of gear smoothly, (I don't know anything about I/O's so thats something else to look at), Do all the electrical items work, does it have dual batteries with a selector switch, any corrosion on the battery terminals, test bilge pump, does the bilge area look clean or greasy/grimy, do you smell mildew, Hull condition (blisters in the gel coat/deep scratches), If it has a trailer does the trailer have bearing buddies and do they have grease in them.