My wife owns a training & consulting business as a sole proprietorship. The business is based in Texas but she delivers her services nationally and internationally. Does she have to file state income tax returns for the services delivered at a location outside of Texas?
if she was in the other states to deliver her services, those states would probably require her to file an income tax return (just like ballplayers).
on the other hand if she delivered the services from Texas, for the most part no. however, some states have telecommuting rules which could subject her to their income taxes.
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.