If he or she wants rewrites I have no problem doing them. I just don't want someone I don't know and who doesn't know the setting, the characters, and the history of the setting poking their nose in it. If it is a person who knows the material, which is there is only 2 other people than myself, who can believes he or she can improve a scene or two then I have no problem with it.
It requires them to know 700 years of history that leads up to the events in the screenplay, but I am perfectly willing to go into detail for them.