Almost any time you sell something online, you are supposed to charge sales tax for sales to people in your state. Quite often, people from these states buying online our are actually supposed to fess up and pay the sales tax on ANYTHING they buy online from out of state on their own (its usually called a 'Use Tax' or some such thing) but really, who does that? For some states, your sales tax is based on your physical location (where you physically sell at a show or where you ship from - Origin-based sales tax) but others you pay sales taxes based on where you sell TO (where your customer is having the item shipped to -Origin-based sales tax .) As sales taxes can include state charges, county charges, and city charges, there can be MANY different actual tax RATES in one state. Actually CHARGING the appropriate rate can be a serious pain, as Etsy for example has limits in its software that make it very hard to set it up appropriately when you have different rates based on zip code! Your state BOE or its equivalent will tell you what your state requires.
For someone doing Art or Craft shows in a different state than you reside in, you need to contact that state's BOE and be sure to get the proper paperwork BEFORE THE SHOW. Although in the shows I did in California, I never actually encountered the BOE Rep, they were rumored to wander shows asking vendors for their paperwork and there WERE times the show promoters required us to show proof we had a temporary license to collect. These were fairly simple to get, back in the late 90s you filled out a form, sent it in with info on the dates and locations, then they sent you back a paper to fill out and return after the show and the proper tax chart for determining what you need to charge, as well as a blank form for the NEXT show. For California, we had to file at the end of the month a show was in, but I found it easiest just to file right after a show.
Did I mention this whole thing was a pain in the anatomy?