I agree with Scott that they typically don't get very many hours, like most boat motors here in Rochester. I have found the single biggest problem with those carbed 4 strokes is that they rarely have Sta-Bil put in them and the carb gets fowled with varnish. Count on a carb rebuild. Other than that, it's no different than buying an old outboard, seals, fluids and filters.
A GMC 3/4 ton pick-up with a Western Pro plow would be a better choice...
