For me, I don't know what kind of proof you want, as I've nothing but an email that is sent to me, and maybe the order history from Amazon if you would like so.
The only thing that I can provide you with that can make you feel more secure and believe that it's legit, which I would do privately; is the reason I bought this and kept it for ~3 months and why I would sell it right now, if you like so (but only in case that you're actually interested in buying and not just "curiosity") please lemme know through PM.