Here is a Q & A piece from the revenoors that 'splains this "use tax" business. Lots of luck in collecting it, you bureaucrats! They can collect it on cars, because when you register a car bought out of state, the tax folks require a bill of sale and they will then know that you paid no Alabama sales tax. But how they gonnna know what you bought on eBay?
http://www.ador.state.al.us/salestax/cutax.html