Now you are at the end of the hand and a common mistake is to fold or call with too many hands. If you did not make your draw, it is appropriate to fold regardless of the pot size. However, if you have a mediocre hand and the pot is substantial, you may occasionally have to make a "crying call" although it is very likely that you are beat. Once again, you must use your best judgment though sometimes there exists a fine line between folding and calling on the river.
You will not be bluffing much on the end, unless you are heads-up and quite confident that your opponent was drawing and/or had a weak hand and a scare card hits. Be prepared to fold a good hand if a flush and/or straight card hits and your opponents begin to raise.