Being a invention of the british, the etiquette is very important in the game. The audience is one of the most mannered and polite in the world of sports as they are dead silent during the points. You can literally hear a needle drop. But after a winning stroke, the audience usually breaks out in a massive cheer for the winner.
Although the big tournaments have experienced judges along every line of the court, mistakes can be made. But tennis players are known for being honest and often correct the judges even if it means that they will loose the point. This is one of the reasons for which tennis is reknown for being a gentleman’s sport.