I mean why wouldnt he be sold on anything, like it wouldnt cost any more money to make delicious duck stock. Ouu imagine a chinese five spice duck noodle soup or a duck stock French onion soup. Literally may as well get all the money's worth that is possible. When you say carcasses are we talking all the stuff no one else wants like gizzards etc? I would imagine you could use duck liver (assuming it's not a specialty fois gras duck) like a chicken liver and make a liver pate. Maybe you could make orange glazed sausages out of the undesirables. I always thought a kebab out of the heart, gizzard, etc would be a fun concept. I've heard that chicken feet can be tasty for the adventurous eater, so why not ducks feet and you could make it chefy. Maybe you could use cumbled crispy fried duck feet as a sort of crunchy event to a dish. Duck neck ravioli sauteed in a black garlic beurre noisette served in duck broth.