Amazon Shipping Question! Help!?

I sold a book on amazon about 4-5 weeks ago and my buyer just contacted me today proclaiming that he/she hasn't received the item yet. I don't know what to do now, but I was very certain that I sent it to the correct address. does amazon have a policy that will benefit both sides, or do i have to pay the customer what she/he lost. it wouldn't be fair though cause i just lost the item that was sold! :(