The for sale sections are not our primary focus. Its not realy part of the core of what OOF is about. It is already very intensive of moderator time and effort.
Some people see OOF purely as a free way of shifting their cars/parts for free - sign up, sell, disappear (sometimes without sending parts out).
We need to put in some level of protection for our members, and our view is that 250 posts should be enough so that buyers can look at past posts and get a feel for the individual before sending money off to an Internet stranger. Personally, I'm not convinced that 250 is enough, and I feel we should only provide a place for free ads to those members that contribute back (not necessarily on technical subjects). But thats my own personal opinion, and doesn't necessarily match the Admin Team's view.
We initially thought that 50 posts would be OK for car sales, as buyers will view car, so less chance of seller doing a runner without suppling goods. However, we have found time and time again, some idiot will post 50 pointless posts in a night, 51st being the ad for his car, before buggering off never to be seen again. So we lifted to 250, as its tedious work to undo the mess these idiots cause.
Being able to 'buy your way' into those sections is against the ethos of OOF, and has always been internally rejected every time we have discussed it.