+1 for post count or mod aproval
Hey i am new here and actually came across this looking for the for sale section. At work i am always dealing with creating deterrents that do not block the desired users.
The post count although easy to bypass will get rid of the lazy spam posters, at least you know the guy took an hr to make a bunch of fluff so he may actually check his e-mails if you want his item.
Another option is no e-mails or phone numbers in posts and instead put a PM contact link in? This way if they want to see who responded they have to log in to the forum increasing odds that they update the post and contribute to the community, again this is a no big deal for most, and guys like me who read more than post we are already logged in.
Another suggestion is forced renewals, so instead of the "bump" post maybe a button the user can hit just to say "im still checking in and it is for sale" I know a few guys have a bunch for sale but hey your getting a great benefit from the forum spend a few seconds every 3 days to click a few links. And if they dont click the link we can assume it is gone or sold and delete the posting.
Finally i found the premium section to be a nice thing, i have not had that on other forums i am a part of, mainly the value added feature of the oasis reports, i am thinking that maybe a "premium members - For sale" typically if you are willing to put some cash in to the forum even if you only have a few posts your less likely to be a flake, and it may be an incentive for others to upgrade because the "good stuff" will be in our special for sale area.