So this is what went down:

UTG (loose-passive fish 200BB effective) opens for 25.
Folds to hero in the Cut-Off (I'm 200BB effective also, image is nitty tag) 3-bet to 75 with red QQs.
BTN (nit reg, plays higher usually, 200BB effective) cold calls the 3-bet.
BB (agro fish, 100BB) cold calls 3-bet.

Flop comes 8-9-10 all diamonds. Pot is 300.

At this point I'm not a happy camper - usually I would bet-fold this all the way, but this flop is just terrible even though I have the Q of diamonds and its 4 way.

Its checked to me - I decide to check it back and see what happens expecting fireworks. BTN bets 100 (! seems small for such a wet flop) BB and UTG muck their hands.

What do you guys think at this point?

well... what was the turn?

Ok sure lets go to the turn.

I call the 100, turn is a total blank (a black small rag). I checked.

Villain bets 275 (pot is 500 at this point).

I think that there is a problem if the SB gets to bet after it has checked all the way around.

Sorry should say UTG checks, BB folds after SB bets 100.

So I will just post river:

Another blank on the river, I check, villain ship all-in.

What? After the flop, SB goes first, BB goes second, UTG goes third...Button goes last.

So either the SB was not in the SB or the SB donked the flop. I am guessing the first and that "SB" was actually the Button.

Ha - brain fart all the way on my part.

Need to edit the original post.

If V truly is a nit, then his range on the river is 88, 99, and TT, and AKdd. Nits are not cold-calling pre with AdTx and not bombing three streets with a draw.

If V is not truly a nit, then 77, JJ, AdTx, and some other hands we beat enter into his range. But you need to tell us whether this is the case. And even then, I am not sure we can give him a wide enough range to justify the call. We need to be good 25% of the time.

I think the turn call may be a mistake. We are getting 2.8:1 on the call but at best we have 12 outs and our flush outs may not be outs at all (AdAx, KdKx, AKdd, AJdd). Our implied odds may also be close to zero, if V is a competent reader of the board and can fold when a four-flush or four-straight is staring him in the face.

He is def a nit, been playing with him for years in different venues. His cold calling range in my mind has to be pairs and AK (I feel that he is 4-betting KK+ almost always).

My reasoning for calling turn - and I was very much on the fence about it btw - was that he could be betting JJ (especially with a J of diamonds) for value and would check back the river being a nit and all. (Also not expected a call from JJ on the river if I lead.) Also he does have it in him to fire a couple of semi-bluffs with the AKo with one card being a diamond.

It seems like we agree mostly in our reasoning on turn and river. How do you feel about not going the standard way and betting the flop?

I find that when I am figuring out what I can beat, instead of focusing on what I think V's range is, that my brain is yelling at me, "FOLD! FOLD! FOLD!" (I wish my brain would actually do the latter and not the former.) And hoping that V will check back a blank river is another sign that you are not in a good spot.

Yes, JJ makes sense with this line pre, flop, and turn. But so do 88-TT and a flopped flush.

My first thought on the OP was to lead the flop. While you are OOP, you have the initiative in the hand. The problem is that you have to bet pretty big ($200+) to force Vs to define their range and that gets you into commitment territory, which you don't want to be in. But check-calling clearly does not work, as we see here.

It's a mess. And when it's a mess, bail. I think that my line is c/c flop, c/f turn. Which seems such a waste. But position really is huge here.

OK, thanks - this makes me feel good about the hand. I ended up folding river and I really wanted to just muck the hand on the flop but I was wondering if it was too weak.

I totally agree with if its a mess bail approach - I'm usually really careful pre trying to ensure getting into good situations and I guess its the same philosophy extended to post.