The bump problem was largely addressed in 2010, when the OP was not allowed to post in his/her own thread except (in theory) as a response to another member. There was some buddy bumping, some price policing and redirecting (The price you're asking is way to high!! Mr X is selling the same thing at whatever site for a whole lot less than yours), and a good deal of argumentative crap - all of which led a lot of infractions being generated in the classifieds.
Personally, I prefer the classifieds closed to posts; with only being open to contributing members being the next best option...but I'm more interested in the well being of the site. I can always go back to locking my ads
If you choose to reopen the classifieds to responses by all members; I'd cast about 30-40 votes in favor of keeping the first block in place, to reduce the number of bump attempts.