I second the quality motor vote. Not absolute way to predict it but just keep in mind a 115 is probably approaching $10,000 new.
Also, I'd get an aluminum boat 17-20' with a windshield and above all else, a motor with fewish hours that has been maintained. Anything that has spent lots of time in the salt I would stay away from unless someone takes unusually good care. Look for corrosion signs.