if it's a league match or a match that is being played for anything other than fun, why don't you have line judges?
I may be in England, but when I used to play tournaments or matches at my local club or against other clubs, we always had officials or line judges to make sure no cheating went on.
I think it's a bit of a joke that sometimes grown men and women can't be trusted to play a tennis match without making a few bad calls, but when there is a lot at stake it always pays to have someone keeping an eye on things.
I have even known cases in the past, before officials were present in our matches, you would get people watching correcting bad calls when the ball bounced in or out and has been called different, which is always nice.
it can be hard sometimes when you are concentrating on hitting the ball back over the net to see exactly where the ball has bounced.
these ended up being the people who became line judges (for a small fee)