If they fold to half pot cbets, does that mean they fold to full pot vbets? When they call, are they that much more likely to fold for twenty extra cents? (You bet half the pot anyways...)

I bet the turn too (You can has pairs and draw too).

Him betting the river kinda sucks, but there are a lot nines or two pair hands he could have that he'd bet b/c you took the cbet/give up on turn line looking line. I'm not sure I would raise here though.