All good players bluff, it is all part of the game, and the skill in playing, is to read the other player, and spot his bluffs. I have on many occasions, spotted bluffs by other players in live games, as there are somethings that you can spot, that cannot be mimicked.
A nervous twitch, a racing pulse, even which way he looks when he is about to bet, or after he makes his bet, all tell a story. Your job is to spot them and make the right decision. One player I played against on a regular basis, always looked at his chip stack, when he had hit the flop in a big way even before it was his turn to act, because he was trying to think how much he could make and how much he should bet, but if he had missed the flop he would stare down at the table as if he wanted the cards to magically change in his favor.
Sometimes I get it wrong, but that is why I keep practicing, but in some circumstances I make a calculated guess and take them out of the game.
Poker would not be fun if people didn't bluff, a favorite phrase you must have heard of is"getting caught with your hands in the cookie jar" (when a player is trying to steal a pot by bluffing). The hard part is not getting caught.
On-line it is so much harder to spot bluffs, as the physical tells are not available to you, and you have to depend more on your gut feelings, recently when the flop dropped two Spades and a Heart in a game I was involved in, my opponent raised pre-flop, bet the flop, checked the turn and went all-in on the River, my first reaction was to fold my top pair with a good kicker (A/K suited) when he pushed all-in, but when I thought about it, I decided that if I had the nuts, would I push all-in? and the simple answer was NO! I would be betting maybe half the pot to get a few more chips out of him, I called and he had exactly the same hand. (split pot).
When the fun Stops, STOP!
and it's fun.
