It's been 8 days since I've registered, and I still can't post in the marketplace. Village Genius told me that there's a 4 day waiting period, but it has been twice that period, and I still can't post??
Post count is not a factor in this, the only requirement is being registered for four days.
You are in the usergroup that has permissions to post in the marketplace, I do not know why you can't do it. What error message does it give you when you try to post a new thread?