Coming up against blatant cheaters can take the fun out of tennis. It takes personal discipline to give your opponent the benefit of the doubt on line calls and I teach students to do so by telling them when in doubt call it in.
I think most know bad calls and cheating in tennis is a problem that is hard to solve. I've had adults and kids that I"m teaching make calls for their benefit that were obviously wrong. When I see it I talk to the whole group by having a quick line call clinic. The cheater knows I'm talking to them. In social tennis, you'll be ostracized eventually so it solves itself.
In competitive tennis, you need to take an active effort to stop it. If you have blatant cheaters probably the only way to fix them if you are the opponent is to point out your doubts on calls first, call an umpire, and if they persist, return the favor with obvious intent. A cheater can use such actions not only to take points but to break your focus so you need to find a way to fight them on it without putting yourself at a disadvantage.
The bottom line is that cheating does work for cheaters in competitive tennis so you can't just let it slide. You have to use every means available within reason to stop them.
1. question the calls first.
2. request a judge
3. quietly make it clear to your opponent that you won't be cheated out of a match and if that includes returning the favor then I'd liken it stopping a thief from stealing.
Maybe someday we'll have AI robots that can solve the problem by making calls for every court. Until then, letting a cheater win only makes you a loser.
You have to act or accept the loss.
