When you hire a mediator you expect someone to come in with experience and humility. Not someone who walks on water and claims to be your savior.

They can say they are not expert but just there to give ideas and give your group the space to work through the difficulties.

A good mediator will ask for feedback on how they are doing. Even better, listen to that feedback.

A good mediator will know that when conflict happens some will want to fall back on rule making, do power moves,  try to find who is right and who is wrong. 

Lastly, a good mediator will know that it takes courage and growth to form a community and that structures help but the hard work is just starting.

I have a friend who is a mediator and he cracked me up by saying some want to dive into the issues and other just want him to move his projector over an inch or so.