The basic necessary features specific to Pro are:

For sellers (back end):
-Every seller can manage his/her separate inventory, customers' wish lists and order history, set up their own tax rates, discounts and coupons.
- sellers pay commission to admin on sales.
- sellers sign up with an account which can also work as a customers account.

front end sellers:
- sellers have own public page with only their stock listed, as well as a banner/heading and profile description (similar to x cart mall add on).
- sellers public store page has its own unique url (www.mall.com/sellersname)

customers:
- shipping costs per seller are displayed as part of the final total in the shopping cart and on check out.
- customers can search for sellers (like brands/manufacturers) like they would other categories or products.

Admin
- the administrator/store owner manages general store operation, configuration and perform maintenance. Collects commission on sales.
- makes the site attactive, and works on cross links with blogs, other websites to generate SEO.
- maintains a linked blog.