1. In singles, my friend hit a ball that he thought caught the line. His opponent went up and looked at the mark and said it was definitely out. Before my friend could walk up to the net to take a closer look, his opponent wiped out the mark with his shoe! 2. Same friend is playing doubles. His partner serves and comes in and puts away a floater. No call was ever made. Their opponents claimed the ball was out. When asked to produce the mark, they could not. Still, the opponents would not yield the point. 3. Same friend is playing doubles. His partner serves and comes in to put away a floater. The returner yells back, so his partner just catches the ball with his hand and goes back to hit a 2nd serve. The other team claims the ball was in, he was just telling his partner to step back because of the bad return.