When you're putting together a private sector team, you talk to players, parents, coaches, scouts and friends. If you don't know what you're getting, you find out.
I have been a coach, umpire and organizer in several sports for a lot of years. If you're talking a short tourney run, I'll agree you might not get as good a pool of information.
But if you're going to be together for 3-4 months, on the road a lot, usually under at least minimal stress, you want to have at least an inkling of what you're in for.
It is my experience that a good parent group will police itself if one gets out of control, so the umpire and/or coach won't have to do anything. In fact, it is often good policy to have a GM who takes care of that kind of situation so the coach stays out of it.