I reckon you're short on bullet point 1 by 20 posts, so bullet point 2 seems an option:
New members will not be able to use the section for selling until they are deemed to be active members, this will happen after 30 days and 30 posts.
If you can't post because you have not reached the new member threshold, you can send the seller a PM. Sellers can add the PM received information in the thread