Snapcall, you just can't ever fold a flush, even if it's 9 high flush

he probably had AJ, you should call

I prefer calling OTT with your combo without a good villain specific reason. Its the worst flush you can have and you can have tons of them, at this board.

Villain also has a lot of flush combo's OTT, so I wouldn't snapcall. That said, I probably do call eventually.

I do think its reasonably close.

Against a nitty opponent, you might consider fold it, because it's reasonably close.
This opponent, how ever, he is pretty loose preflop, and his cb % is relatively high.
Against this type of player, I would never consider folding 100bb stack with a hand like this.

I assume he is not a player who plays straightforward postflop. He steals a lot, maybe thinks a lot. That's the difference with a nitty player.

yeah theres also lots of hands he could possibly do this with that are worse,
Acx AA JJ AJ also a few worse flushes even a random 34

and 30/21 is very loose

I don't think it matters if anyone ever raised as a bluff or not on a monotone board. Only very few would bluff this board this way, OP really looks like a flopped flush. That's why I personally like to raise flop.

Does villain raise his sets & 2P here? that's the better question than if he's bluffing or not