It may come down to a choice between your preferred "light touch", Cristiano, and plain old business.
It's a decision only you can make, but if I were you I'd start with charging a small fee for any merchants who want to post in any of the SLU Classified sections, unless they're already a paying advertiser.
That would include New Product Listings and Commercial Announcements.
I think it's admirable that you want to help the community but I don't think you should be expected to foot the entire bill yourself. That only invites people to take advantage of you.
"As long as thereís one person on earth who remembers you, it isnít over." - Oscar Hammerstein