[Scooterdoo]

Didn't read all the replies so perhaps someone (or you) mentioned this, but if he really had a better hand it is very unlikely that he checks the river after you checked the turn. He's a good player and wants to get something out of the hand and cannot be sure that you will bet. Also, he has not shown much strength and he knows that you know that he's a strong player capable of betting with air, so a 1/2 to pot sized bet could easily get called by you even if you don't have much. Plus he would be thinking that perhaps a bet by him will bring a big re-raise/bluff by you. It just doesn't make sense for a good player to check the river with a 3 or a full house. Oh, well.