From my experience, the really bad cheaters are the ones that only do it on break point or match point. Happened to me last week. The first time he did it I got him to reverse the call because the ball left a ball mark. But on match point in the 3rd set at 4-5 40-30, my ball landed a good 6 inches inside the line and he called it out for the match and he wouldn't change it, even though everyone watching the match agreed that the ball was in. He has been reported to USTA with corroborating testimony from others watching the match, but I doubt anything will happen to him because he is ranked highly in the state and has been around for a long time. It really sucks, but there isn't much you can do about it.