It would be better... However I think the problem with it's own sub forum (I think that's what you mean) is there's not that much volume going on. About 1 post per day on average, and that might go down if it's outside of the action on this forum.
I would suggest to try adding "Gold Members Only" to the Headline of the current Buy and Sell. Currently this rule is a bit hard to find for new people, they have start on page one, read your rules, then click the little "here" link and read the rest of the rules. ....Most people including myself are lazy and don't actually read the rules. When the most important rule is loud and clear, you'll cut down on most infractions, and more non moderators will also start stepping up and policing. If that step is taking and it's still a problem, then take more drastic action.
....This is assuming there's no way to set a post as gold members only can post, because that is the easiest fix.