Do you sell membership on your forum, how do you get paying users. Are they paying enough for you to be able to sustain your forum? I was able to sell membership to just one user on my last forum, and interestingly, he was an administrative staff.
I've never done this on any of my forums before. I did have a VIP group on a Sonic forum I used to own but you didn't need to pay to be promoted, you just needed to reach a certain number of posts.
