Member sells, keeps profit, pays subscription fee?

Hi,
Subject basically says it all. I need to allow members of my site to sell their own documents and have the money sent directly to their account. I don't want to collect commission on their sales, but would like to charge a small membership or subscription fee for allowing them to sell through my site. This will not be a multi-vendor/virtual strip mall setup.

Will it be possible to only charge a subscription to members who sell while allowing all other members a free account?

Are these things possible with any combination of your extensions and plug-ins?

Thanks in advance.
boogs

Disappointing there is no response to a simple pre-sales question. If by Monday there is still no response I'll be looking elsewhere for what I need.