Hi! I just sold two sets of books to a buyer. She paid me thru paypal but I went to USPS myself to drop off the package. She received the package 1 week later however the envelope was torn and taped, and that there were stickers saying "Received item unsealed". It was just weird that she received the envelope but it was empty though.I tracked down the number saying the item was dropped off at her front door. She sent me pictures of how she received it. I also have pictures of the tracking number receipt and the sealed package. How do I go about this? Thank you.