Villain is a breakeven/marginally winning player on SS on a $3K downswing atm.

So far, I'd characterize him as moderately aggressive preflop but weaktight postflop. He checked back a lot of flops in position (in both limped and raised pots) and folded to bets on later streets, and out of position he folded to most cbets and donked 1 or 2 flops. He'd put in a couple of 3bets so far, but this hand was the first one I'd called down.

I defended A9 here because the frequency of his 3betting was going up, so I'm guess that there are lower pocket pairs and KJ+-type hands in his range now. Also, he's started acting faster, and seems to be (subjective judgment) a little frustrated.

I obv love this flop, but for someone who'd been cbetting ~1/2 pot, this cbet size seemed a little too large. If he's cbetting 100% of his range like this, it's an easy shove, looking for spazz calls from AT+ and having A outs vs. over pairs, but the betsizing felt weird enough that I'm not certain if he's cbetting his entire range the same here.

I can't see a fold here, but is a call reasonable? Or should I just be shipping always.

Thoughts?

Well the simple answer is to ship, always, because so many turn cards either kill your action or give him the best hand. I can't see calling to induce a bluff because we don't really know what his range will look like on the turn if d, 7, A, or some other straight completing/overcard hits. It's nice to have the read that he's frustrated and more likely to be bluffing here but we can end up getting ourselves owned pretty often if we just flat and then make the assumption that he's unbalanced when any scare card hits. And pretty much everything is a scare card on this board. I should also mention that I don't really love defending with this hand to a 3bet. We can't be too happy when an ace hits. It can't be too bad if he's 3betting 20%ish and he's bad post but in general my cutoff would be like A9s and AT against someone decent 3betting that much.

Also, had he been cbetting all flops 50%? It's generally better to cbet a little larger on these flops.

We hadn't played a 3bet pot yet, so I don't know what he does in 3bet pots. In single-raised pots, if he cbet, he cbet 1/2-pot.

I was referring to textures. Was he cbetting 1/2 on a JT7ssd flop?

I read that this was your first defend in the opening post and just assumed that he'd size about the same in 3bet pots as in single raised. Regs tend to cbet smaller in their 3bet pots, fish don't change their sizing based on stacks much if at all.

Sorry I wasn't clear - I was saying that he was cbetting 1/2 independent of texture.

And I think you're right about defending A9. I think one of my leaks is defending to 3bets too liberally. Usually I hand-wave a justification like "oh, he's been 3betting so often", but I often find myself in tricky spots because of it.

How low do you go with pairs when defending against an "average" 3bettor? 88? 99? Do you defend KQo? Or is it better to throw in a hand like 89s vs KQo, that'll be dominated by his range less.

I guess the answer to the 89s thing is that it depends on stack sizes. And the deeper you are, the better of a play it is.

Nevertheless, I still find myself struggling sometimes to construct good defending ranges in-game.

The main things to consider are what they're 3betting with and stacks. If they're 3betting really polarized then I prefer to 4bet more than I defend, if I'm defending it's usually because we're deep and with some sort of suited connector or broadway hand that doesn't have sick RIO and can hit more than just top pair. If they're 3betting wide then I'll just defend/4bet the top of my range relative to their frequency and sometimes toss some suited connectors in just to make sure I'm not totally unbalanced. The deeper you get the looser you can defend in either scenario.

But to answer the questions on specific hands - against a lot of players you can 4bet 88+ or 99+. Pairs are largely dependent on your postflop skill level and effective stack size and your opponent's aggression. The better you are postflop and deeper the stacks and more passive your opponent the more inclined you should be to defend them. I'm flatting against almost all 3bet ranges with KQ. In HU SNG's I'm sort of a nit when it comes to 3bets though. The stacks are really shallow and nobody seems to 3bet much anyway.

Just shove,he has a PSB left on turn if you call and doubt he will be ever bluffing in that spot.