Quote Originally Posted by Fnord
~$140 in the pot

Turn is

Opponent gives me an evil look and starts to reach for chips, then checks. I think about it for a bit then check behind.

River is

Opponent seriously considers a push, then announces "$100."

I pay him off.
These two actions, clearly says that his bluffing most of the time. If he feels you as weak (even if he has no reads on you) why would he show so must aggression and then first check on turn and bet 2/3 OOP on river?
(This is a clear strong means weak in Caro's book )
With this aggression you would only push with a huge hand.
Unless he is a very good player I think you good here most often.

As for turn, due to the same reads during this hand I would also check.