[Plugin: Another WordPress Classifieds Plugin] Multisite

AWPCP can be activated on a per-site basis. I am not a WPMU expert so it will depend on how your installation handles that. I have it installed on a multi-site install but activated only for a single site. So I know it can be done, but apparently my host does it a little differently than others so whatever I tell you may not apply. You’ll probably need to speak with your hosting company about it or get a WPMU expert involved.