[deception5]

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Assuming someone has a flush on a three-flush board is one thing, but most of the time here, you are beat.

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I completely agree with your statement. You are beat here very often. But it's still worth a call because if the pot is 19BB you only need to win 5% of the time for your call to be profitable. Surely someone will bet out here with a worse hand than a flush that often, think about how profitable the bet was in this example.

This example was unclear as to the size of the pot, but the poster said that he raised furiously on the flop and turn leading me to believe this pot was large. Even if it was only 10BB you still need to win only 10% of the time. It also makes a difference whether it was a monotone flop or not (giving odds for anyone with a single card of that suit to call down).

Also, according to Clarkmeister's Theorem - if you were going to call a bet on the river here it's far better to bet yourself. You may fold a better hand and it is extremely likely that you would be raised by anything but a flush. So it's possible that the player is betting out based on this concept.

Finally, the probability of one of the 2 players having a flush card:

52 cards in the deck minus 2 hole cards minus 5 board cards = 45 remaining cards.

9 flush cards out there still so the chance of all 4 hole cards in the 2 players' hands being non-flush

(36/45*35/44*34/43*33/42)=39%

meaning the probably of 1 or more flush cards being out there is 61%.

It's slightly more likely that someone continued because of a flush but even so there's a good enough chance that we are not against a flush to warrant a call here.