My comments: I would not mess with what you have now -- seems to work fairly well as a start. The volume of ads here is very low compared to some other hobby sites, but it could grow and get some legs if you do not bow to pressure to overly regulate it.
I think so long as everyone pays a nominal fee for an ad as you have it now, it is not a good idea to try and distinguish "dealers" and "non-dealers" -- this is a very dicey value judgment and fraught with conflicts of interest.
Getting the quantity and quality of mechandise being sold to a higher level, i.e. liquidity and volume is important for classified ads to work.
The most critical policing of the ads to be done is to try to eliminate non-authentic seller/buyers attempting criminal fraud with PayPal or money order schemes (etc.). Another hobby site I belong to (www.astromart.com
) has been great at keeping con men out and making it a safe place to buy and sell gear. You might want to examine their techniques.