Effective stacks $100 no reads on villian.

1. UTG raises to $3, CO calls, I raise OTB to $12, blinds fold, UTG folds, and CO calls.
2. Flop [9d][4d], pot $28, CO checks I bet $20 and he calls.
3. Turn , pot $68 he checks I check.
4. River , pot $68, CO leads for $55. Hero?

I used to think this was a very trivial call, but is he really gonna show me AQ or KQ [of non-diamonds] enough here to make this call +EV?

The problem is I don't even see what can be bluffing here that I beat. If I do call this and my AA is good, he has to have horribly misplayed a street. This still happen enough at this level to warrent the call?

Yeah just because all the draws (JT and diamonds) got there on the turn, it's tough to find many hands you're ahead of. I suppose a weirdly played KK/JJ/TT are possible in addition to AQ/KQ.

There are a ton of donks out there.

I probably call this most of the time, but I think I agree with you, it may be a -EV call over time.

I call for sure here...the bluff % is so high here, as is him making a semi-bluff (something that he would bet that has showdown value).