Maybe this forum is not the best place to sell such account? There might be more specialized forums in the net.
I don't think any forums are capable to sell Steam accounts safely and easily, since they're not allowed by the company the account was registered in the first place. I may be wrong though.
You are right though as far as i saw, while selling that account, these accounts are traded. Might be that steam is not going after it so aggressive or that these trades happen more silently or so.