If this is player vs player, then this is pretty bad form.

Player B knows about the sense motive roll to spot a bluff that he made and failed, then the player is using that meta game knowledge about the other player's bluff, that his character would not know about, having failed the opposed check.

This is about as against the rules as casting linked perception to improve the party's spot and listen, because the player knows he just failed a listen check. The character does not know he failed the check.

The character does not know he failed to spot a bluff, And so does not know the feint is coming. It's really bad form for the player to use that knowledge.

It's touchy (!) if the player can claim he would have withdrawn anyway. But it smells bad to me.

Esp since Able is in worse shape 2HP than Barlo's 5HP. Why would he withdrew from the fight when he's about to win with his next blow?