there are 2 sections for cars for sale - this one is generally board members and one off users that come to advertise, mostly US and Canadian sellers. once in a while we see someone from Europe, Australia, Asia, etc come on to sell. The other section is labeled for Ebay/Craigslist - generally these are ones other board members find and post up, mostly random and the same scenario of mostly US/Canadian and a few overseas sellers.
as for how folks list, there are no rules, just folks posting how they see fit. personally, I always try to put a better description in the header (Year/Make/Location/Price) so folks know what they are getting into before even clicking the link. but that's just me, everyone does it a little different.