I used to think that the good players and the fish at the table could be spotted very easily. I've recently noticed that sometimes it's difficult to spot pros, and what at first may seem like a calling stationy-spewy player, could actually be a good lag, and also vice versa. Poker is a complicated game and not all is what is initially seems.

VPIP and PFR are good indicators. Besides stats you can check if player is emotional and making bad calls trying to revenge for previous hands. This is sure sign he is no shark.

Also if he is trying to win every hand and going to the river often, you can be sure he is no pro.

The best indicator is what kinds of hands they are playing when you see them at showdown and seeing how they played on each street with that hand.
Bet sizing, VPIP and PRF stats are also very good at giving you some idea what you're up against.
But you are right, poker often is not at all what it seems and can be a very complicated game to figure out and definitely is not always what it at first seems.

I often play tournaments for free. There you have a lot of players who bluff and play on luck. If you start quietly, you will notice those players and you can play them away with good cards. Of course you still have the chance that they are very lucky, which is very frustrating.

This is true, and sometimes players with a unreasonable preflop strategy AKA "fish" can be somewhat tough to play against postflop. And other times someone, who seemed to be a solid TAG or LAG, will make the most crazy calldown postflop, because they were on tilt or something. At the end of the day you always need to respect your opponents and try to objectively figure out, what they are doing wrong, that you can take advantage off. Its not as simple as "LOL this player is a fish, so I am going to win".

There is a player on one site that I play that has a tendency to play loose fishy in a way that causes the good players to have to play extremely tight to beat them. They accumulate a lot of chips from their actions until the ones who know how to be nitty or really good TAGs get the right flops. I have never seen the person make the final table, but many times I have seen the person as a maniac fish. It took studying how they played to figure this out, especially because they were inconsistent. There are also nitty fish who do the opposite. They play only when they get an A, no matter the kicker. You really do have to play many hands with people you do not know to gather the information needed to see what type they are.

no one is immune from mistakes. even knowledge of psychology will not always help ...

Originally Posted by fundiver199

This is true, and sometimes players with a unreasonable preflop strategy AKA "fish" can be somewhat tough to play against postflop. And other times someone, who seemed to be a solid TAG or LAG, will make the most crazy calldown postflop, because they were on tilt or something. At the end of the day you always need to respect your opponents and try to objectively figure out, what they are doing wrong, that you can take advantage off. Its not as simple as "LOL this player is a fish, so I am going to win".

I could not have said it better.