[soah]

You must consider your equity against his entire range of hands. Sometimes you will lose money. That is unavoidable. For each time that your opponent has a flush, how often will he have a hand which you beat (which will pay off a river bet)?

Suppose you lose $8 on the river when your hand is no good (your opponent raises and you fold) but you gain $8 each time he calls you with KQ, etc. How much do you gain or lose ON AVERAGE from your river bet?

Compare this to what happens if you check the river... most of the time your opponent will check behind with weakish hands and you gain nothing, but he will bet the hands that beat you. Are you confident enough to fold though?

Until you can estimate reasonable probabilities for what your opponent might hold and what he will do with each of those hands, you cannot determine for sure what is best. All I can do is tell you that you must look at the big picture, and not get caught up in individual hands.