USPS can be a pain. Only experience was with an international shipment on a MR item. Acrylic cover got damaged in transit. USPS refused to do anything because buyer didn't take the item back to his post office to document the damage even though he had sent me the pictures which I then sent to USPS. We had to go round and round with USPS for at least a month until they finally paid the insurance, which buyer had paid for to insure for purchase price.
I don't bother with ebay for selling any more. I have found FB marketplace to be much easier. I have sold everything from a few Hasbro figures up to more expensive MR items. Haven't had any troubles.
At this point, it feels like you almost need to take a video of you packing the item in a box, sealing it, and putting the label on it for shipping. At the very least, you have the the receipt that shows shipping zip code and weight of the package so he can't say you shipped an empty box.