How should one deal with people who cheat or have bad sportsmanship? There is a simple answer which would make this article very short: call for an umpire. However, umpires are not always available (and most of your matches will likely be practice matches anyway, where there are normally no umpires), so sometimes you’ll have to deal with this on your own, especially if it’s only poor sportsmanship, not outright cheating. Besides, you don’t want to call for an umpire every time you think an opponent looks at you funny, so when possible, deal with the problem on your own.
Cheaters cheat because they want to win. There are limits to how you can deal with this short of calling for an umpire. If the opponent simply calls the score wrong, the remedy might be to simply call the score out loud every point, so the score is absolutely clear to you, your opponent, and anyone watching. Cheaters don’t like this because it’s hard to argue about the score when it’s been called out loudly and clearly every point.