We have all seen poker professionals staring one another down looking for subtle tells in high stakes poker. This sort of player to player interaction has made live poker what it is today, an extremely popular spectator sport. The best players in the world claim that they can get hints on their opponent's hands by watching the pulse in their neck or the way their face reacts to certain circumstances or even the way they put their chips into the pot.
When playing online poker there is obviously no face to face interaction. Some poker professionals claim that this takes some of the skill out of the game. Poker professionals that rely heavily on opponent tells seldom do well at online poker. Some claim that online poker is more of a mathematics game rather than a people game. To some extent this might be true, however, I believe that online poker tells are still there, you just need to know where to look. In fact, if you look closely you can come up with a whole new sets of tells.
Time between actions
As with bricks and mortar poker, the time it takes your opponent to act may reveal something about the strength of their hand. For example, a long pause and a bet usually is a sign of strength. A long pause and a check usually is a sign of a weakness. The above rules I have found hold generally, however, better opponents may vary their strategy so make sure that you watch each opponent carefully to get a read on them.
Online poker brings an added feature that bricks and mortar poker rooms don't have – you can click on buttons to automatically make your decision before it is your time to act. For example, you can click on check/fold or bet/raise and when the action is on you the software will automatically play according to your predetermined decision. You will often see 5 people fold in less than a second because they have all clicked on the check/fold button.
You can deduce lots of information about the strength of your opponent's hands by observing when your opponents have clicked on the check/fold or bet/raise buttons. For example, after the flop if you check and someone behind you instantly checks you can bet that they have a poor hand and have clicked on the check fold button. A bet in a future round is sure to get them to fold more often than not. Similarly, if you bet into someone and before you can blink they have raised you, you can bet they have clicked on bet/raise and have a solid hand. Similarly, if you are behind someone who has obviously clicked on the bet/raise button you will need a strong hand to keep going. These two tells are unique to review poker online and I believe they are strong tells.
You can usually assume that players that always take a reasonable time to act are doing other things. They could be surfing the net or playing more than one game. You can bet that these players are not giving their full attention to each game. You can often raise these players out of pots, particularly if they are tight.
The chat box
Online poker allows you to talk to other players in the chat box. Here is the rule: Generally, the more a person chats the worse they are at poker. This is something I have observed to be true through hours of playing. Also, players that abuse other players in the chat box are usually very poor players as well. After all, why would a good player abuse a fish? The only thing that this will achieve is getting the fish to leave the table. Sometimes these players are so poor they will tell you what they have got in the chat box. Sometimes it is as obvious as "I have trips and I don't want to be outdrawn by a flush again" or "come-on heart".
Posting out of position
Players posting out of position is a tell in live games as well, but because there is so much more movement between tables in online poker it happens more often. A player that posts out of position is nearly always a poor player. Similarly, a player that waits until it is his/her big blind, or when they have the button, before posting are usually good patient players. This tell is fantastic because you can often get a read on players before they even play a hand.