BTN: $19.42 (194.2 bb)
Hero (SB): $9.85 (98.5 bb)
BB: $36.73 (367.3 bb)
UTG: $10.71 (107.1 bb)
MP: $28.16 (281.6 bb)
CO: $18.93 (189.3 bb)

Preflop: Hero is SB with 5 6 A K
4 folds, Hero raises to $0.30, BB raises to $0.90, Hero calls $0.60

Flop: ($1.80) K 8 T (2 players)
Hero checks, BB bets $1.10, Hero calls $1.10

Turn: ($4) 6 (2 players)
Hero checks, BB checks

River: ($4) 3 (2 players)
Hero checks, BB bets $3.40, Hero ?

BB 29/20 3bet:7 af:2.6

Im thinking that 4betting pre might be pushing a small equity edge. As played I would call the river.

I would not 4bet this hand against that 3bet %.

Villain bet is polarized, rarely will have a better 2pair+, since we will be betting all ours flushes here, I think we should call this as std, only folding against passive players

Villain never has better 2p here, never has sets as these hands will fire the turn w/ so many draws out there he could be extracting value from. He's probably checking this turn back to realise his equity and not open himself up to getting x/r on this turn which a lot of better hands and big semi-bluffs can do, putting him in a tough spot.

When we check to him again on the river, he can now value bet his flushes and bluff us with a lot of his air because our range looks so weak, and we can rarely have a flush in this spot as we'd probably be betting these our self.

You're right Mindead in that this river bet is pretty polarised. Flush or total air here. He might actually be showing up here with air far more often then flushes though, because he may have barreled this turn card if he picked up equity w/ a decent flush draw. w/ that knowledge I am probably calling this river.