They don't have to prove anything. You do. When the 'proof of purchase/receipt' info doesn't match the name and address on the warranty request, that's a good sign that you're not the original buyer. If the warranty states 'original buyer only', pretending to be that buyer amounts to commiting fraud. Some products may be covered for the warranty period, no matter who the owner is, but it would have to be stated in the warranty info.Makes sense if you send the manufacturer a warranty card in with your name on it, if you don't have to send them one it should transfer fine; how can they prove it changed hands?