different areas have different rules concerning when it is necessary to have a license. you really have to check where you live to know when it is required. the town i lived in- if you wanted to have a booth and sell at a festival in town or even the holiday craft fair at the school each year you had to have a DBA.
you have to follow local laws concerning when they require a sales tax license if you live in a state that has sales tax- some areas if you sell more than 5 items in a year you need the license, some areas it depends on other things.