I post regularly on two sites, this one and the other one. I initially joined both sites to sell stuff, believe it or not.
I had thousands of dollars in tackle I amassed over the years and wanted to unload it all, which I did. Over time I met alot of guys from both sites and made a lot of friends, which was a much bigger dividend for me than simply joining the site to sell stuff.
Also, the BST rules have necessarily changed a bit as more people are visiting sites just to buy and sell, thus the number of issues related to buying and selling have increased since I joined in 2003.
Over time I got more involved, but I still view the BST as a reason to visit, meaning if you're a fisherman you're always looking for discount tackle deals if you're like me.
As long as the people selling stuff aren't getting carried away, I wouldn't do anything...perhaps they'll become regular contibutors over time. The amount of buying and selling here isn't that great, so I'd leave it alone but monitor for signs of abuse.