There's really nothing you can do or even respond. The whole thing is weird. Taking the packaging to the PO is really meaningless if the buyer simply removed the contents anyway and is just trying to make it look like he is "doing the right thing". 

If he was really serious, he would have opened a dispute instead of running around like this. But then again, there are plenty of buyers that we see on this forum who honestly have no idea how to do the most basic of things such as opening a case. Right now, I wouldn't even mention the option to them at all.

As I mentioned in a previous response, they are probably just fishing for a refund. They just haven't worked out how to get it from you yet.