One of the risks of having a for sale section is the enormous number of people who would join the forum just to post something.
I don't think we should go there. This is a discussion list, not eBay. Most of us know how to use eBay or other for sale sites.
A "wanted" section would be useful - maybe set something up like a "swap meet" thread for looking for, swapping, buying and selling hard-to-find parts. Maybe if the thread title was "Swap Meet" instead of "for sale," that would be better?
The only thing I can think of to try and limit the "riff raff" would be to somehow avoid having the tags put it out on the Web in all the search engines. I am very low-tech but Muhammed might be able to figure out how to do that.