The problem with charging is what we are doing now. Why rent a classified when there are MANY was to let people know that you need, want or sell on other sites, forums or message boards.
Carnies are even using Craigs List!
It is now well established that the web is free for all, except us site owners. People now expect everything to be free just as in the early days of television...there was never a charge for your local channels.
Back in 1996 (ow, that hurts to say that), in the old days of the internet I charged for certain areas of my website at showmen.com and then later carnivalbiz.com. Probably made $100 a month for a couple of years...but it was slowly coming to an end.
It is a pretty simple proposition. If you have a very successful site, you can attract advertisers that want to target your specific topic. It is working for many and working well. The big gain comes when you are so successful that someone wants to buy your site...that is when the big bucks come.
Of course, I will be watching Matts experiment eagerly but I have some doubts...I hope to be proven wrong!
BTW. Ritchie mentioned in several of the above posts also frequents my site. No big deal. He leaves an ad. I review it and post it. One ad at a time. Ya gotta be fair to everybody thats in the business.
That said, I know pompous carnies like me are annoying, but what the hell.....once in a while a gem of wisdom comes out of our mouth or keyboard.