Yea, this gets messy.
You also have to charge customers local taxes if any apply, and give them to the state/county, which also means you might need a business licenses / tax permit for some locations.
I see this at conventions in my home state. All the venders, even from out of state, have to get and display a business licenses, along with a "sales and use" tax license issued by my state. Out of state business licenses are not valid.
The mobile techs I see on YouTube seem to state within a state or region, like Oregon /Washington so they don't have to deal with too many tax districts.