I've played several hands recently where I PFR and my heads up opponent would checkcall the flop and then bet the turn and river, and then flip over a strong hand, usually TP or better (but less than straight or flush). Analyzing the hands, most of them did it when a 3rd straight or flush card hit on the turn, so I'm guessing they were planning on checkraising me but instead decided to protect their hand with a bet.

Any postflop reads on opponent?