Guest players happen a lot and for two reasons. One is ok, one is sketchy as [lacrosse].

A team adds a tournament as an extra and needs to have a guest or two to fill out a roster to play because their team wasn't complete. this isn't so bad but it usually isn't in season and certainly isn't the bigger tournaments

They also invite guests to try to improve. If this is the case, and your son loses one minute of time, move on. It is your son that they are trying to upgrade from. You paid the fees but the greener grass is getting the time. go to a program that doesn't invite guests!