I think to get the most out of the for sale section there will have to be a slightly different policy to speakerplans. The free for all that it was ended up not working in the end.
What were the problems over there?
1. New users signing up just for that section. Not a problem in its self but when you get idiots signing up and entering transactions who don't have the common sense or decency to complete them satisfactorily it doesn't really promote a safe environment to buy and sell in. Having to contribute to the forum a bit before you start buying and selling means at least people get to know you a bit. Ideally you want a nice forum for nice people where there can be trust between the members. I think a minimum post count of say between 30 and 50 would at least help to ease the situation.
2. Commercial sellers. Personally my biggest gripe. I am not talking about people like the two Tony's who offer products to members at prices that they wouldn't normally have access to. I mean people who own or work for company's that ONLY post to flog items at the going market rate or reply to wanted posts (GDS anyone?). I am not really sure how to overcome this, I think stricter moderation is the key, maybe having to approve new threads.
I also think if you are selling high value items you should be prepared to give a little back to the forum, say anything over £500 and 2% goes back to the forum, similar to blue room. Again this is hard to police and requires more work but it does generate a small income so could be worth it.
My 2p.