I seriously need membership plugin

I’m about to launch a website that works like a classifieds/jobs site, and I already have a shortlist of the theme(s) I would use. However, all the themes I have come across lack a feature I consider very important for my business model.

I need a plugin that would allow “users who wish to sell” to register and post their items on my website.

All the membership plugins I’ve come across only allow limiting access to posts or content, and not access to functions. I would appreciate anybody could point out a plugin that would answer my prayers. Premium and free plugins are welcome.