All the for sale ads...

My vote is for a totally separate forum for the stuff for sale, and another for the wanted ads.
Would be easier than pretty much anything else, and that ability is already in the forum software.

If I have something for sale it goes in the "Parts for sale" section, and obviously if I was wanting something I could put a want ad in the "Parts Wanted" section.
Oh, and obviously not shown be default in the new posts or main page of course.
There could even be sub sections for different types of parts.
Engines, Transmissions, Body, Interior, Other.