Did you take a picture of the label? I had this issue before with an overseas buyer. Claiming I sent empty box. I went and submitted my shipping label to eBay showing the weight of the parcel. At the end eBay ruled in favour of me as a seller.
Another way to protect yourself when it comes to selling expensive item is that you take video of showing goods in box, packing in post office and film until the parcel handed over to counter service. This is the most extreme way I could think of.
