I am overly fair. My wife *****es at me for playing serves that seem in to me but she (a spectator) can see them as out. But this happens all the time, ya can't get every call right.
I'll only hook a person if I KNOW that they've made the wrong call on purpose. Such as a doubles opponent who is right on top of the line, the ball is clearly in and he calls it out. I'll wait for an in ball and call it out. What goes 'round comes 'round.