I'm incubating test eggs for a friend/former customer. I get first pick of the chicks, plus he is letting me use his two hovabators to increase the amount of space I have for hatching! He has been a very good customer and he's good at picking up on time. I've gotten a few new breeds from him this way (cukoo marans and polish for now). I enjoy hatching, and I don't charge him.
Anyone else, I would charge a minimum of 25 cents per egg if the egg is mine and 10 cents per egg if they brought them to me. I would also get them to sign a contract saying that I cannot be held responsible for deaths, especially infertile eggs, bloodrings, or genetic defects. I will hatch test eggs for free (to see if everyone is fertile), but I keep any and all chicks resulting from test hatches.
If someone doesn't pick up the day after the hatch, they will incur a 50 cents per day, per chick feeding/watering/cleaning up poo fee. That really helps out with the whole picking up chicks on time. If someone doesn't pick up their chicks within a week (unless extrenuating cercumstances prevent it, these are case by case) they go up for sale. I sell mixed chicks for $1.50 and pure blooded chicks at $2.50.
Right now I have too many of my own chicken and duck eggs in the incubator to take on anyone elses at the moment. lol.
Oh, I also candle before I set any eggs, do not charge for cracked eggs (because they don't get put into the incubator), and I mark air cells. I also keep records on daily temp and humidity, if I turn by hand what time it was when they were turned, anything found while candling (infertile, bloodrings, etc), and set, stop turning, and projected hatch dates. Yes, I do keep up with this on paper. I've had too much info lost when our last computer crashed to trust one again.
All I can say is to get any customers to sign a contract (we don't need any lawsuits over someone trying to get you to hatch infertile eggs) and keep good records! Always inform your customers that accidents happen, and always be honest. If there is a certain chick that you want, contact the people you are hatching for and offer to pay for it.
When you're trying to figure out how much to charge, think of how much electricity you're going to be using, your time, and if you have to pay for city water, how much water will you be using. Unless you already have brooders, heat lamps, feeders, and waterers factor in those expenses as well. You won't make any profit for a while, and even when you do, it probably won't be much, but if you enjoy the incubation and hatching process, it's well worth it. Plus that little bit of profit will help pay for food for your animals!
Most of what I've learned of dealing with the public came at my own expense and learning the hard way! I used to raise gerbils of all colors (even the near impossible to find schimmel!). I kept a pair for someone while they were on a trip, and I charged them I think $15 for the week to care for them. Something happened and their 6 year old female died while in my care, and she just so happened to have new babies. I fostered the babies to one of my females and tried to call the owner. Well, to make a long story short, she got extremely upset about me fostering the babies and demanded them back, even though she did not have a way to care for them at that age. We got into an argument, and I gave her the babies back with their dad. Needless to say the babies died, and I started getting nasty phone calls from this woman. Anyway, I'm not in contact with her any more and I have contracts now on nearly everything, just to cover my own tail!
Always remember, everyone is human, and everyone forgets things. That's why I'll hang onto the chicks for one week before they become my property. I try to contact (phone call, e-mail, etc) at least three times during that week. I can't keep extras usually, so they go up for sale. That is plainly stated before I start the incubator.
You also may want to charge a small batch fee, since running the incubator will cost the same whether it has three eggs or 30 eggs in it. I will typically fill the empty spaces with my eggs, since I can sell the extras and it helps to keep the humidity and temperature from taking wild swings.