Are you sure? This is the typical semi-polite way of responding to a questionable line call. No matter what our age, players don’t always possess great eyesight, and they are simply calling it as they see it. Unfortunately, players don’t engage in the art of giving their opponents the so-called “benefit of the doubt.”
In the tennis professional world (ATP/WTA) that’s why Hawk-Eye was created to assist with the linesman call, as well as players overruling whether the call may be correct or not. Now, on the other hand, there are some out there who make repeated bad line calls (cheating or just plain bad eyesight), and some will do whatever it takes to win a point (thumbs down!).
Be mindful, tennis is a game that should display good sportsmanship and fairness to others. It’s okay to overrule yourself or your partner and switch your call. Apologize, keep it fair and friendly, and ultimately avoid the “eye for an eye” of “I’ll get even with you” situation. This could lead to the game affecting you mentally when your opponent starts giving you bad calls to retaliate. This display will certainly test your patience during play, and you must remain calm and in control of yourself to stay mentally strong and positive. Remember, a person who has good character is someone doing the right thing when no one else is around.