Well, the admin makes the law on this forum!!! If he says there's no way to SPAM then there really IS NO WAY.
On the other side the 'sell or buy' section might not be the way that became very useful for a vendor because the posting will fade away more and more with each new posting on that board. A static side would be the answer but it might be a little bit more work for the admin.
You can locate a link under your subscription, so anyone see your link and will follow it if he/she thinks that your comments are good and qualified...
Greetings from Frankfurt (Germany),