Speaking as a seller I would hope that any duty would be paid by the customer one way or another before the goods are shipped.
Many years ago I had a boutique where I purchased items from a wholesaler that he imported from England, unfortunately he fell on hard times, long story, and went out of business. He gave me a heads up that there was a shipment from England that he would not be making his credit payment for the shipment or paying the duty at customs. The goods ended up at a Canada Customs auction where I bought them for pennies on the dollar.