If your partner in good faith calls a ball out and you are certain it was in, you are cheating if you do not tell your partner you disagree so she can give the point to the opponent.
That said, if I am standing on a line and am in better position than you are and you overrule me or tell me to give the point to our opponents, I will box your ears. All you people who like to call the far sideline when I am standing right there take notice.
If you are in a bad position, then you cannot be certain a ball was in or out and you should trust that I *did* see it. If I didn't see it, I would ask you.
I swear, most of the time when I see partner disagreement is when somebody is calling a line they shouldn't be calling from a poor position.
-- Random Error Generator, Version 4.0
-- Master Moonballer