As for charging sales tax more than once, I believe that its not illegal as long as you remit the tax to the state. A good example here in PA is the sale of a car. If I bought a car last week and paid sales tax on it, then decided to sell it this week, the purchaser would pay sales tax again to the state based on that sales price. One thing for sure, every state is different. Also, you often get differing info from officials in the same state.