Sadly you have been taken for a ride.

Never post to any other address other than the one on the paypal payment notice

You should refund them and tell them to change the details before they make the final click to pay.

Call ebay and ask them to read the messages where he has asked to send the item to another address and see if they can take action on his account as this might bring them to the attention of ebay to see if they are doing this to other sellers.