[JohnG]

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Four players see a flop of J [img]/images/graemlins/diamond.gif[/img]5 [img]/images/graemlins/diamond.gif[/img]7 [img]/images/graemlins/diamond.gif[/img] and it is checked around. I was last to act - should I have taken a shot at this pot here?

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Usually not.

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Is he calling to set me up for a river bluff?

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I doubt he bluffs the river (in general, not knowing the player). You could easily be strong.

I probably just call his small turn bet rather than raise. I don't see much value in escalating the pot size on the turn, given the board and our hand.

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River is the A [img]/images/graemlins/heart.gif[/img]. Big stack pushes and I am sick. I really am confused now.

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You tested him on the turn. He passed the test. You could easily have a strong hand here. If the river bet is a big bet, I'd normally give him credit and fold.

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Was this a very weak fold considering I would be a huge chipleader if he is on a bluff and I win the hand?

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Not sure it's a good idea to be habitually putting players on bluffs in that spot. I think a strong hand is much more likely.
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Pretty loose call by 22 preflop, given your position relative to the raiser, but maybe ok.