Gambling

Both players make a Bluff check versus the opponent's Sense Motive check. If they succeed on their bluff they get a +4 on the next roll (which will determine the round) but if they fail they get a -4 on the next roll (that's true for both players). 
Then to settle the round both players make a Profession (Gambler) check (with the bonus or penalty) and winner takes whatever was bet. 
There's one exception, because Profession requires you to be trained, if someone was playing and not trained in the skill, they would just make a Wisdom check instead but would only be able to benefit +2 from their bluff if they succeed (they still get -4 if they fail). This makes it so people who are trained in gambling have a clear edge over people who don't.