Do you mean like posting commissions or items you created as a submission?

Advertising commissions are okay as long as it's not just all text and you have an actual image that's not in violation of the rules. As for an item you created, it would depend on what you created. I don't think we ever had a specific rule against advertising in submissions. Just anything in the submission would have to be acceptable with the rules of the ToS.

Of course if a person was interested in selling something, we would appreciate an ad being taken out on the site, which helps to support the gallery. It would alsoy get seen more than a submission that would roll off the page eventually, so an ad would be better for the person looking to sell as well.