Yes I have had to pay duties on items (records) imported from Europe (to the U.S.). The U.S. does not charge duties on products originally made in the U.S. and "re-imported" from Canada or other countries, but paperwork still needs to be filled out. Except that very few home theater items are made in the U.S.
In the U.S. all states with sales taxes also require that residents purchasing goods from outside the state declare the purchase and pay a use tax which is at the same rate. The use tax is reduced if a sales tax was actually paid to a different state or country.
U.S. tourists driving back from Canada or Mexico (or returning from anywhere) must declare purchases made abroad and pay duties. So I expect that items ordered through the mail are also taxed.
In all my purchase transactions the seller took care of the paperwork and collected (charged me) the duties/taxes. Otherwise the item could be held at the border for the buyer to come and get. I expect that I would have to do the paperwork if I was selling something out of the U.S. However a U.S. seller is not obliged to collect state sales taxes in state to state transactions unless the seller has a store or office or warehouse etc. in the destination state.
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