While inter-city and state shipping in the U.S. via USPS is very inexpensive, especially if you ship in quanitity, U.S. to Canada shipments can be double the cost of Canada to the U.S. shipments. I recently shipped a product there that had to come back and the shipping cost (legitimate) was double what I'd paid to ship to the U.S. So if you sell something for $100, and it costs $20 to ship, you could see yourself with a $40 return shipping cost, essentially and probably wiping out any margin on the original sale. The ideal scenario would never to have to take a product back, but that's not always possible. In a case like that, a discount for the buyer to keep the product (partial refund) or even (depending on the circumstances and costs) abandoning the product and just giving back the sale price might be the best option.