This happened to me, as a buyer, on eBay. The item was shipped and I never received it. The seller was so nice, even went to her post office and opened a claim. She offered to refund my money or send another. I opted to send another and she said if I received both to just mark return to sender on the duplicate package.
As a buyer, it made me feel good that she was so willing to help. And you can't help but feel a bit guilty because you know there are people out there that aren't honest and will try to get another item for free. The fact that she never accused me of being dishonest was, to me, sufficient evidence that she is a great seller and I gave her mad props on her review. Just going the extra mile is worth it. One of my best experiences, even with the item still not being here. Good customer service is where it's at.