It’s a common scam.
But something, weight the box with a brick or rocks, the return it for a full refund.
Retailers should open the box and do an inventory before issuing a refund. But, most don’t.
Same thing some eBayers told me. Buyer returns goods via USPS with tracking, saying "not as described". Seller opens box and finds rocks or other filler and yells "wait a minute!" eBay/PayPal says "Tough Noogies, tracking shows you received item", end of story.