I am one of the moderators on Smokstak, and most of the time I have very little to do, as Harry Matthews (site owner/operator) has always had a very rigid policy on new members and members causing problems.
To keep a site running takes time and money, even 'static' display sites like our own take up a considerable amount of time, facilities and cash.
Working out which policy to adopt towards new members is always going to be time-consuming but if done properly, it will repay the initial input many times over.
I suppose it is a 'growing pains' sort of problem, as it doesn't rear its head until there is a fair bit of traffic and that's exactly when you don't have time to go in and start making policy changes.
Personally, I'd be inclined to make new member approval a matter for a small panel of existing members, and let them decide. Plenty of them have the time and access to do it, just needs, say, a minimum of three members to approve a new one. THEN you can go to registration etc., when you know you have a good member in prospect.
My 2c worth.
Peter