I hear because of the feathers, it is alot more time consuming than chickens. I just did 16 Cornish/ Rock Chickens and I would not be excited about defeathering 4 ducks.
I have been trying to find someone around Mn that would do it for me as well. Did 2 chickens and was not pleased with the process (but I am willing to try again). I was hoping to delude myself into thinking the birds were going to the next farm- hard to do if you are the one dispatching them...