If you are talking about small scale, I would say it is almost impossible to compete with the hatcheries especially if you are buying hatching eggs in to incubate, rather than breed them yourself.
The following are some things that occur to me off the cuff that you need to consider....
I would imagine that the majority of people want sexed pullets rather than straight run or the option to return/exchange any cockerels. It doesn't sound like you would be in a position to offer that option.
If your hatching egg supplier isn't local, you are likely to have a lower hatch rate due to eggs being scrambled in the post.... that will really eat into any profits.
If it was financially viable to do it, the breeder who is supplying the hatching eggs, would probably be doing it themselves to make money.
You have to be prepared to deal with the casualties that will almost certainly occur from time to time because the more you hatch, the more likely you are to have some sick/malformed chicks.... are you going to want to spend time trying to fix them and will people want to buy "gimpy" ones or be prepared to cull them?
Are you going to offer them vaccinated?
Can you ensure your power supply? If you are talking about rarer breeds, the eggs will be more expensive and a power outage at the wrong time could really wipe out your profits.
Are you prepared to deal with difficult customers wanting refunds etc for chicks that die, which might be as a result of their poor management or maybe poor quality breeding stock, which would be difficult to establish once the chicks leave your care?
I have to say, it has to be kinder to the chicks to be hatched and sold locally rather than sent out mail order, with all the associated stress, so from a welfare perspective, more people doing this has to be a good thing. Whether there is any chance of a profit in it is another matter.
Good luck
Barbara