You have to check the rules of each individual state. For the most part, if in order for the business to deliver it's product or service to another state, it requires the physical presence of the business, the business owner, or an employee of that business in said state to provide the product or service, then the income earned during that physical presence is subject to taxes in the state where the product or service is provided. Additionally, the state and many of the locales in said state usually require the business to registered to operate in that state and/or locality. This is especially true if the state and/or locality taxes personal income.
