Not great spot because all overpairs are in his range and he's not really bluffing this turn/river, but A9 I'm still calling there as my bottom range, i would fold K9-down.

On the stakes where people are starting to think about ranges its super easy call just because we dont really have TT+ in our range and therefore A9 is really super high in our range there.

I would fold vs unknown. People don't triple barrel bluff at all at NL10, specially on such runout. I might call with reads, like a high WTSD and low W$SD, or big barreling frequencies

Raise flop is a viable alternative especially since in BvB people don't like to give up easily so it's very possible that you are gonna get floated by AQ AJ AT and if that A hits the turn BOOOOM it's value time baby.

As played im snapping him off OTR because he should be bluffing some busted FDs and im high up in my range. And even if he doesn't bluff I'm winning the times he checks behind his bluffs so my longterm EV in this spot can only be ruined by folding (and therefore losing to his bluffs) whereas if I call I only have to worry about TT+ which he will frequently have especially if he isn't bluffing but it's BvB so I wouldn't say as a default that people aren't bluffing.

But obviously fold if you have a read on this guy that he doesn't bluff river.