grannyring
Show me where it says used items are taxed. Only retail sales are mentioned.The term "retail sales" includes the sale of used items between private parties. I'm not sure why you think otherwise. In any event, the proof you seem to seek is in the OP, silly:
... I bought a used amp from a guy in Canada through A’gon. But I paid the tariff on it. Now they also want tax."So he has a tax bill from the taxing authority, under the terms explained on the state website. If you think used items are somehow oddly exempt under Tennessee tax code, I’m sure the OP will be grateful for the appeal you’ll file on his behalf. When filing an appeal in a tax code dispute, you'll need to cite the exact language in the code that supports your claim. Good luck with that!

