I've often thought a programmed set of questions to post in the firearms section would be helpful. An automated box of required questions (rifle or pistol, location of seller, willing to ship, price or trade only, C&R eligible (y/n/uncertain)). It would probably require each firearm to be in its own post within the thread.
Then, once these are answered, every new posting has a box that lists these. It would eliminate rule breaking and make it much easier for people to size up the situation.