[tessarji]

I would 3-bet.

I feel his most likely hand is a high pocket pair or A9 that is raising the river for value, banking that he's usually ahead and that on this scattered board you won't have a 3-betting hand ever. He doesn't put you on a flush because you 3-bet preflop which contraindicates suited cards in his mind.

I think he will usually pay you off with several hands less than a flush.

I'd call a four-bet because he is a spaz.