The main aspect on the success of an ecommerce site is justifying people to go check it. A site can be excellent and even so be empty, because never got enough traction. Sellers don't waste time listing anything, because they know there won't be enough buyers.
In this case, the platform is integrated on the wallet (if I understood correctly), therefore it's much more easy for people to check it, but even so, since it's beta, I would make it free (just for now).
Listing will always be free, as will creating your own web store. I'm also going to have it so sellers can import from other sales channels etc ebay, amazon etc
Ever thought about Craigslist?
Thought what about it?