I'm not so sure this is a defend pre.

I really instinctually hate c/f river here but understand what you say that there's not a lot of hands he's bluffing here. And he could be checking back flop with Q or K high non paired spades.

Are you only folding river cuz his sizing? Because if you are c/f to most any bets... Leading river is far superior imo.

I thought i should call pre since there was a rec player in the pot, but i could be wrong. One reason why i am check folding here was because of his larger sizing. I didn't think he would be betting smaller flushes this size? And the other reason was ya because its hard for him to be bluffing.

If i were to bet the river myself what am i expecting him to call with? I'm not sure he would call with less then a flush. The only non flush hands he should have that possibly could call are qqxx q6ax, possibly some set that he checked back the flop (although i think he would bet that OTF, and there aren't that many flopped sets in his range pre i think?), and these hand probably fold river if i bet.