I write this article to help many poker players to distinguish a bluff from a real hand, I have heard many people say, but it seemed a bluff, or I would´ve win that hand.
I start saying that if you do not have a hand and you don’t have a read of the player (s) against whom you are playing you should not put them in a bluff, believe that he has the best hand and you will save a lot of chips.
Most of all bluffs occur when the tournaments are well underway, many players are intimidated by an all-in, or a raise on the flop, even pre flop, and I will share the way I think and read opponents to see if they have a hand, I put the following scenario:

All remaining players are cashed in, you're in the BB with 15BB and you are holding A-5 of diamonds button raises 4 times the BB with a 30BB stack, you call, the flop is:

At this stage of the tournament there are several options with this flop, with more reason that is a heads up (on this particular scenario) I never check if I hit a pair on heads up, a check is a sign of weakness, even doing a check-raise depending on the situation, what I recommend is a continuation bet equal to the POT TOTAL, with two clubs on the table, we have to consider what the opponent is doing next:
When he only calls: I love to play the bluffs as if had an awesome hand (this case AK of clubs) so regardless of the turn, I bet as if you really have A-Ks and I bet according size of the pot, I bet the  half of  the pot as a minimum, if the turn is another club, I may repeat the bed, if he calls regardless of river, I bet 3 / 4 of the pot, if I go up there and the turn and river are over cards or a club doesn’t matter, because you are bluffing anyway, if he has the K he will call, if he gets the flush he will call as well, usually if you're playing a tournament buy-in of medium to high, they will fold if they don’t have at least top pair with a decent kicker, at this point you should have a read over your opponent, I recommend attention.

Now you have to be careful if the pot is getting too big and you don’t have a hand and you don’t have many chips left, is time to stop betting and fold if opponent bets. In very weird occasions you can play a 3 bet or an all-in depending on opponent, you must have a read for this and do not do it against chip leads.

If I raises me: Can I now believe the K Because of the Presence of the 2 clubs he wants the turn as expensive as possible, I will check Probably, unless There's another 5 or an A (Unlikely to Happen)

Let's change the flop a little bit.

You bet he raises: Usually at this flop the player is bluffing or has a set leads, or a pair over everything on the table, why? Because if he truly has a K why he will raise? There´s no flush or straight draw, if he wants my chips, he will just call. I usually do not re-raise because he falls in the same reading that I have over him, just call, the turn is not over but a 2 of hearts, you show strength with a high bet, if he re-raise again, he may have the K or A-4which is unlikely since you have an A in your hand, I call nothing else in the river can get one over but be firm and believe that K, a flat scarier call, is worse than a re-raise or a raise, besides protect your chips, on the river if you have a strong read over him and there´s no high cards, an all-in will do the job, at this point many, many players  fold right away, but once again you have to have a read of the player.

You bet, he calls: in this case if he has a read over you and I hope he does, he knows that you hit something, so will probably be careful too, if I get scared to continue with the bets I do a pot control check as soon as I can, if he bets, depending on the bet can call, but is be very cautious and try to apply the maximum pot control at this point and once again, is too important to read the opponent.

Against aggressive players you need to be careful, I am one of them, but to be a successful aggressive player must be very good on the reads, or try to apply the maximum reading, I am one of those that hit the top pair on the flop and I bet strong or I say all in, so they do not believe me top pair, again with a proper reading of the player.

Bottom line a player who has a hand won’t probably raise on the flop unless there´s a flush draw or straight draw.
And when you are bluffing you need to have a read under your opponent and don’t do it too often, they will get you.

I hope you find it interesting and see you at the tables.