I used to do about 30 days worth of craft shows a year. This was about 20 - 25 years ago (before hubby & kids), and while I still worked a full-time day job. I would guess that I was able to earn about half as much from the sewing as I did at my day job.
Downside: I was REALLY TIRED. During the busy pre-Christmas season, I'd work all day, then sew till 2 am, drink a full cup of coffee, then lie down and immediately fall asleep. My alarm clock was set for 5 am and some of the caffeine was still in my system, so I could get 2 1/2 hours of sewing in before leaving for work.
I don't think that craft shows are as good now as they were then. "Country clutter" was still in vogue, and there weren't as many Chinese imports as there are today. Meaning that I don't think I could be as profitable now as I was then.
At the time, I made braided wreaths, little stuffed animals, Christmas ornaments, baby bonnets, table linens, and appliance covers. I still make the last two items, but now I sell them online instead of at craft shows.