I'm not sure. It sounds smaller scale to me, as I have encountered people on Craigslist with bigger flocks than that selling eggs and chicks. But just because it's on Craigslist doesn't make it legal lol.
I guess at the end of the day, if this is going to be a business venture for you, you may want to look into an LLC or something. If you just think you'll have excess eggs and want to sell them for cash on Craigslist, then no need.
I should add that I am no expert at all. I'm just speaking from what I've seen sellers online doing.