I think being able to delete advertisements would be nice. I often post an ad saying that I want to buy something and then I'm out of money or I already bought it and people still message me about it.

Deleting isn't for spelling, html errors or anything, just for taking down your advertisement. It would leave space for the current ads that are still valid.

One rule I think should be placed in if this idea happened is that you still have your posting limits, even if you delete. You put up 2 advertisements, your limit is 2, you take down 1. You can't post another at this time because you exceeded your limit.