AJT9ss flopped nf - deep

As villain I would fold flop. It's single raised pot and I wouldn't feel obligated to call pot raise / incoming barrels with third nuts or even second nuts. You might as well have 2 straightflushes, so his hand is 5th nuts and quite easy fold.

Difficult spot otr. You could bet river as thin value with reasonable sizing, as he could call with his flush bluffcather thinking why are you betting this river. But it could induce our villain to turn his hand into big bluff. I think checking is fine,if he bets huge very hard decision. I would probably just fold, villain needs to be aggressive to turn hus SHV into bluff.

Villain was bluffcatching, so makes sense to just check-back. You could give up now with A-blocker.

I think you should go for blockerbluffs, maybe avoid them against fishes. Here is couple of things though: it's deep, so we're risking more (+ side it's harder for him to call down), you dont have nuts with A-blocker, you give bad price so utg/flop continuing range will be strong.

If villain should be folding a queen high flush on the flop then doesn't it make sense for him to check that hand back deep? After all, he's never getting 3 streets from worse.

Also, if he must fold a pretty strong hand otf ( relative to all the other hands he might continuation bet) doesn't that make him a bit exploitable?

What should be his bet /call down range?

Yes, IMO it would make sense to xb his hand this flop.

I just think defending his hand here will not end up making profit for him. Therefore I would maybe even little exploitatively let it go. I dont think too many players will go with huge sized blockerbluffs this level such spot deep. And his hand is obviously more valuable when there is no possible straightflushes.

Also you're defended vs utg, I think your range is more heavy towards NF than blocker, while you certainly can have some of both.

Just my 2c's