Black Jumbos! When will you be selling hatching eggs? Do they breed true? How much will you sell the eggs for?
Information for a Jumbo Coturnix color addict!
As for killing, I use a sharp pair of kitchen scissors. If you don't care about the skin then cut off the head, let the blood drain out, clip the wings and work your finger into the wing hole between the flesh and the skin. It will peel right off for you. The first few times are a hassle. After that you can usually peel it all off in one piece. I salt mine and save them to sell later or use for crafts.
Once you have the skin off, cut a small hole beneath the breastbone with the scissors and pull out the innards. I separate mine out: some go in the edible bag and the rest go in the bait bag. I plan on making a mean gravy, soup or something once I get enough hearts, livers and gizards collected.
If you do want the skin saved, you can either dry pluck or boil the quail for ten seconds - be careful not to overboil. Plucking is pretty easy, which is a blessing and a bane: the feathers come out fine but the skin is delicate and tears.