Slightly bigger pre.

Check flop! C-betting the flop is super spewy.

As played, call turn; call river.

I decided before calling the turn I was never folding the river. Shoving the turn is out of the question for the reason he'll fold his bluffs and call when I'm beat. A flat call (especially after genuinely thinking for a while on the turn), gives the rec player some hope I'm not that strong and will fold to his river barrel.

Once I called the turn bet, I don't see how I can ever fold ANY river. If I decided he was not strong on the turn, how can I think things changed and I'm now beat?

It's certainly true that the river is unlikely to change anything. Probably only a 6 or 9 would have possibly helped you there by counterfeiting his A3. I also wouldn't want to see a straight card as he could have a straight draw with 54 or 87.

Going back to the OP for a second: villain raised/folded from early position on the first hand you played, and then 4 hands later (this hand), he calls a raise from BB and donks the turn. Other players here seem to be loose-passive (typical for these stakes obviously) and I wonder if this guy is the table LAG (of unknown quality at this point). I know sample size is small but there's enough here for me to think this guy might have a wide range of hands here and is capable of being agressive with a draw or crappy 2 pair here.

So, anyway, it originally seemed close to me between folding and calling, but the more I think about it the more I am OK with calling down given that he obviously is capable of some aggression altho we don't have much clue how loose he is or overall how good he is given the small sample size. But I think folding to this guy assumes he is more of a typical loose/passive sort than the evidence indicates. I mean, I expect to lose here pretty often, just not often enough to fold.

Also, I'm not sure we should ignore 96 or 63 here. Discount yes, but with the info we have, these seem possible and also could make the river card bad. Not an uncommon call from an loose unknown in the BB.

But possibly I am biased by recently seeing 53o win 3 big pots in under an hour by making 2 boats and a straight...

Have to call it off now. I hope your spidey senses were correct. The rec players I come across don't bluff very much, and if they were to bet that A, they could be AQ, but maybe we have different player pools. Most rec players I come across would just call down w/ an A.