I shipped an item without insurance (it was a $10 item including shipping) and the buyer says the received an empty envelope with a tear in it. It was a piece of plastic for a treadmill that weighed less than an ounce, and it was wrapped up in paper towels for cushioning and placed in a regular business envelope. The seal was double taped for security. Apparently one of the postage machines ripped the envelope open. Would you refund the $10 (I'm leaning towards this option) or do nothing because the buyer opted out of paying for insurance?