Bang for your Buck! Having real value and not just taking your money. Providing real, honest feedback about your son's abilities, and not sugar coating his deficiencies. I have a great relationship with my son's coach, and I'll be honest I haven't with every coach he has ever had. I have developed a great relationship with this coach, and it started early on because of a disagreement that we had. I was impressed that he listened to my issues, and we were able to talk about it. Some coaches will not listen or talk about issues. To this day, I believe I was right, but I had a lot of respect for him for taking the time to talk.
It is also important for these coaches to know the right people, and be respected in the baseball community, because as you will find, it is a small community. If they have been around the game long, they probably know a lot of people.
Also, making sure the coach has your son's best interests at heart and aren't just consumed with their own agenda.
Son's coach provides good insight, instruction - on and off the field, understands when we have to pick and choose events, because I am not rich by any means, etc.