When a player is one break ahead before the end of a set
Here is a situation that often warrants a quick bet on the outcome of the next service game. When a player has managed to break the other guy's serve just once and the set approaches the end, at some point that player will be two games ahead and will need only to win his own serve to conquer the set. The player who is behind serves, and he needs to win his service game to stay in the set and possibly re-break the leading player's serve to tie.
In such a situation, the player who is one break ahead will very often focus on his upcoming own service game. He may not just let the other guy's service game go, but he often won't put in the last effort. For example, you may see him play the returns more aggressively, hoping to win some easy points.
That player will be even more inclined to do so if he had no trouble winning his own service games so far.
This is, in consequence, at time where you should take a close look at the odds offered for a service game won by the player who is behind - chances are it is going to be an easy game for him. And if it works, place another one on the leading player winning his upcoming service game, and the set!