The mallard is the ancestor of almost all domestic duck breeds except those derived from the Muscovy duck. The Rouen duck has the same plumage as a wild mallard and its meat reportedly has a somewhat stronger flavor than white feathered breeds. Perhaps that's what's being sold as "mallard". It looks just like a mallard and many people call it a "domesticated mallard", but a true mallard is a wild duck. As such, its sale would probably be strictly regulated (or possibly even prohibited) by game laws.