How you know when you have to fold the top pair and there is not any magic trick, which can allow you know while you are behind, however you do not require one. Ask one question when you play online casinos for real money. Is this spot where I will make some money against the opponent?
Till your answer comes "YES!" -- say, that you are up against the maniac who already has check out the raised for the stack, as well as you are set to beat him in a pot with the chips, and then there is generally not anything totally wrong to play tighter, and rather than looser.
What it means for the top pair kind hands is very simple and you would like to make money with the top pair (ad against most of the players) by having value betting, initiative, as well as getting named by the weaker hands. How you know when you have to fold the top pair? While you are no longer the value betting against the opponent with the weaker pair, then this is one very good indication the hand that you had wished to play is not a hand, which you are in fact playing casino poker rooms, also you may look at some other choices to play the hand, which includes folding.
Against some kinds of the opponents, particularly the aggressive opponents, and it is OK to call the raises in case, they are probably bluffs. But, against any of the reasonable opponent, most of the money that you would like to put that in with the top pair is around 30 big blinds. When your opponent begins asking you invest more of chips than this, and there is one good chance he has got the beat, and maybe with 2 pair, straight, flush, and set.