The comment about 1 post wonders selling things has bugged me for some time, it's been discussed before. Maybe either a minimum time period has to lapse, or minimum number of posts reached, before anyone can sell stuff on here? When someone's 1st post is a for sale ad you can bet your house that it will be their last too, unless they have something else to sell.
As for trailer manufacturers pushing their wares in other sections than showroom floor, yes it's annoying and the admin team have shown admirable tolerance with this. Even in the showroom section some push the boundaries a bit eg there is a rule that say something like only 1 thread per seller or product yet there are a few hat have started multiple threads in an effort to spread the word or whatever some ad agency as advised them to do. Ignore, don't read and the problem is solved.