I think it's fine the way it is. If someone posts on here just to sell something, I don't see that as a problem. If the seller has a poorly constructed post, no pictures, and a bad description, then the item probably won't sell and the post will fade into obscurity.
If any changes should be made, it should be a minimum requirement to the structure of the selling post itself. Failure to meet those minimums will result in the post being deleted. Repeated posts from the same seller with the same issues could result in a warning, then a ban.