I have an ebay store. I just checked a few hundred transactions. None of my shipments had tax added on other than those shipped in my home state.
As a seller you can set up tax in each state. Each state that has instituted mandatory collection has a minimum threshold, which is typically a combination of dollars and number of transactions at which an online retailer must collect and submit sales tax.
The good and the bad, I don't meet any of the minimums yet, but hopefully some day.
As far as selling used goods, the double tax issue does suck. This is typically a big issue in the used car business.