First post of the new year for me! Two weeks vacation is a wonderful thing.
I agree with most of the posts, that a mod doesn't necessarily have to be an expert. I think having a great deal of fantasy experience and knowledge would almost come naturally from the job, though, based on the other requirements.
Number one, they have to be very active posters. Mods are responsible for keeping discussions flowing. At the cafe, this has become less important because we now have a pretty large group of users. When I first started coming, though, I know Arlo tried very hard to make sure everyone got a response to a new thread. It didn't necessarily matter what level of expertise was used in the response. It mattered most that the person got one. That would keep us coming back, as a board with little back and forth will quickly die away. Thanks for that, Arlo!
Number two, they have to be friendly and supportive of all opinions. A mod should not be someone to heave insults at someone else, although I like having these guys around too sometimes.
I think those are the main two criteria, and it seems if someone's a very active poster, they'll typically know more than the average person, simply because they spend more time thinking about the subject.