Tax ID if you sell

Okay, all you writers out there. Do you really use a tax ID number if you're selling books out of the trunk of your car? Off of Amazon? What's the skinny?

I do pay sales tax on books that I sell in Alabama...I do not pay sales tax on anything that I sell outside of the state...I don't think you pay on Amazon sales...or sales to book stores, etc. because they will pay any applicable charges.

I haven't paid a lot in taxes...wish it was more...that would mean more book sales! LOL