Why not create a system for newbies to pay a fee upon creating a sales thread specifically for Goods, Services, Lending, Auction, Currency exchange boards and Marketplace (alt)?
If possible, include Marketplace otherwise, they will start creating threads in this section.
Honestly, I think this issue is long overdue. It should be a welcome development if only Theymos would implement it. At least it will reduce the proliferation of threads scamming community members. Also, I would like to see a situation where restrictions are placed on posters of certain ranks opening "restricted threads"