It really comes down to how the other player thinks, once you know how they play it's fairly easy to tell if they're bluffing or not. The play back feature really helps, as you review the hand from the other person's point of view and try and understand what they're probably thinking. After awhile you can stick a note on them and have a fair idea on how they play. However there's always those times where you just have to call and hope you have the best hand.