Earlier quoted context omitted.
We operate almost exactly like Etsy or Ebay in this regard, we just don't expose the marketplace to the front end because we offer only a single product type (photo to painting) at the moment. Many of our sellers are listed on Ebay or Etsy too (at higher prices).
So what is your percentage per work?
The plan is to fix to a fixed commission once the new marketplace is rolled out to the user facing portion of the site.