Not to come across as rude, but you have no way of forcing him to pay for anything other than a refund......AND even then if it was too long ago even your Card Company may tell you to pound sand.

Heck, even if he put 1000% money back guarantee- I don't think you have a leg to stand on. You can sue, you will win- but at what cost? You may end up having to serve him in his municipality, you may have to hire a lawyer, and you may even have to prove further that it's not authentic by getting multiple opinions. One mans opinion isn't the word of God.

Be happy if you get a refund.