Cheating or bad line calls rarely change the course of a match. If you've watched as many matches as we have (gpl and Chem.) yes we've seen a handful of late match calls tilt the match or worse make the outcome irreversible. But that's in the minority of matches by the widest of margins. I believe that if the kids/players feel that cheating is prevalent and don't have a strong handle on how to deal with it then they may build in an excuse for losing.
Yea, balls on the line should be called good. I'd rather hear a player say that if they did not hit the ball so darn close they would not have risked the bad call. Then move on to the next point. There are many obstacles to overcome in winning a match. The more a player believes that he is responsible for what happens his actions on the court, and learns from experiences, the stonger player they will become in the long run.
"i thought those were just a little harmless brown bugs, you know the ones take wings and fly? but it turned to be Flees." Fedace