Before anything else, you can skip this post if you play the VOID option. When challenging a play, you should consider first what option you are using. If you play SINGLE, then making a challenge will not be risky so it's okay if you are unsuccessful. However if you play DOUBLE or 5-POINT, challenge a play if you are willing to risk losing a turn or 5 points. If you suspect your opponent's bingo to be a phoney (invalid word), then challenge it. It's okay if it turns out to be unsuccessful rather than letting him get away with a phoney and the 50-point bonus. But if the play is worth only a few points, then you might want to let it go to avoid the consequences. Another thing that you might want to take note of is that if you can benefit from his play, do not challenge it even if you are sure that it is an invalid word. For example, if he plays CROB and you'll be needing his C to play your bingo which is VACCINES then let him play the word. Or if he plays WARF and you have a D in your rack to make DWARF and it gives you a good spot in the triple word score then do not challenge it.