I sell to friends, strangers and at three markets. I try to get at least $5 a bird deposit from strangers. I purposely under sell, so I have some left over at the end of the batch. Those I can use for myself and/or sell at a market. I just finished a batch of 150. I had 120 sold and then took 30 to the market to sell on consignment.
If you are selling under the USDA exemption, as I do, then you must charge per pound. You can't guarantee size,, but a deposit holds a chicken or chickens. I explain to people that birds can die, so if I don't have enough to fill orders, then first orders get filled first and the deposit money would be returned. I've never encountered that, and hope by under selling, I won't in the future.