Most profitable part for me was rehoming them all. Guess I didn't realize how much I was really spending until I wasn't spending it any more!
Truth is, I agree with my good friend
@lazy gardener. Most of us (certainly not all) would be surprised to see that we just about break if we keep careful and diligent records. I had a solid, regular customer base but the plain truth is that egg selling is all I did - I didn't hatch and sell chicks or raise and sell birds for others. So my assessment may be a little unfair.
As with any enterprise involving living things, one illness or predator attack can wipe it all out. Some diseases can be so bad that you really can't start over without extreme measures because those pathogens stay in the environment and reinfect new birds - IF it's even feasible to start over. There are public officials to deal with in some cases. Competition can be fierce - in my town (a rural community) almost everyone around me had chickens and sold eggs.....I had to find a way to make sure that the customers in my community had a reason to choose mine over others, some of whom were my customer's own relatives.
I did it by individually dating every egg gathered: 8/6 for instance, right on the rounded part of the egg with pencil, then cartoning them in order and marking the outside of the carton with 8/1 - 8/6. It was a little thing and just took seconds to do, but in this day of expiration dates written on everything folks LIKED knowing exactly how old the eggs were. Frankly, I liked it too because I could always be sure to use the oldest eggs first. I had one regular customer who made tons of hard-boiled eggs, so she always wanted the slightly older eggs. Another thing I did was manage to sell eggs from my little Bantams. I simply cut an egg carton in half so I had two half-dozen cartons, put little stickers on the cartons, and labeled them "Kid's Meals". Moms of toddlers loved that because they could save their bigger eggs for cooking and baking, and the bantam eggs were just the right size for little ones to be able to finish. I charged less for those too. The cartons appealed to the kids. So if you are going to make money in the chicken business, choose your marketing strategies carefully, be honest and fair in your dealings, acknowledge that you'll have to deal with some stinkers who complain constantly no matter what you do, and for goodness sake practice safe biosecurity at all times.
You've been given some great links. Good luck to you!