So one of the reasons I joined the team was to built a bot that would help with some of the more mundane tasks that the forum necessitates. One of those tasks is making sure that this area is clean. I've built something that will periodically log itself in and check for new threads and responses to the classifieds. I have successfully deleted a few finished and outdated ads and been running it for a week without anything going wrong, so I thought I'd announce that here!
In order to get the bot to delete your advertisement, simply respond to your ad and make the new reply the following:
QuoteSOLD PLEASE DELETE
(No, it won't delete it if someone else responds to your ad with that text

I'm working on adding features, but my June is pretty busy. But I'll be sure to announce when those are finished!
-Matt