Sooner or later everyone who has successfully sewn for herself hears, "You ought to sell that," or "I bet you could get real money for stuff like that on eBay or Etsy." I'm not persuaded that it is true. There's a special mindset needed for selling online, and a lot of skills. You don't just get to sit home and craft. You have to be a photo stylist, photographer, and photo editor; copywriter, bookkeeper and marketing person as well. Instead of making whatever pleases you or a special item for a special person, you have to make multiples, hoping your choice will please people you don't even know. If you decide to sell at local markets and craft fairs, you have to think about displays, schlep the stuff, and be charming to people. Charming is a skill I lack.
I look at what things sell for and what people are willing to pay. I used to make teddy bears. A good bear takes the better part of 2 days to make, and takes special joints and a certain kind of plastic eyes. By the time I'd totaled the costs, I'd invested $20 in a bear that with luck, I could sell for $25. And table rent, gasoline and incidentals weren't factored in. I decided that bear making was not for me, because I couldn't imagine a customer who would be willing to spent $75 on a 14-inch bear. After the first bear, it wasn't a lot of fun, anyway.
Online prices for doll clothing can be depressing. I refined a pattern for years before I could reliably turn out successful doll dresses from it. Similar dresses are sold for $8, and I'm not willing to sell mine for that. A person with a long track record gets $20 for hers. The fit is visibly better on the $20 sheath dress, and it looks pretty much like the ones I make. $20 is a fair price for a tiny dress that can take 90 minutes to make, and that does not include the intangibles such as the time and experience it took, finding the right fabric for the scale of the doll, or presenting it for sale online. Considering the cost of materials and the time it would take me to make something similar, I'd be earning a negative wage if I started at the bottom.
I tend to research things to death. I helped out at several craft fairs and learned that a good display sells mediocre merchandise, a low price deters buyers, and a strong back is essential. A combination dog wash and spring festival is not a good venue to sell jewelry unless your jewelry is dog-oriented. Selling felt masks and Halloween themed jewelry at a gourd festival just before Halloween flopped. A felt mask that took 3 hours to make was too costly at $18, because people came to the fair looking for bargain pumpkins. Elaborately painted and carved gourds were admired but not purchased.
Manning a booth at a craft fair demands a strong back. Sometimes there are wheeled carts and onsite helpers. More often, you schlep things yourself. A low rate for space rental is offset by your needing to provide table, tent or umbrella, and more. If you are serious, you will buy or concoct display racks and stands. You'll devise displays that lift from their storage containers to the tabletop without needing to be put together.
Feedback from lookers and potential customers is stimulating. I found that necklaces I made for myself because I loved them were appreciated. After years of being told that my taste was too sophisticated and that no one would buy my stuff, I found positive feedback delicious.