NEED ADVISE ON AN AMPLIFIER TRANSACTION

I am hoping you folks can give me some opinions on what you would do in my current situation/transaction.
I listed an integrated amplifier here on Agon, a gentleman purchased it and I boxed the unit as absolutely bombproof as possible. From looking at the buyers other transactions it seems he is somewhere in South or Central America as he has a shipping agent in Miami that receives his shipments, and then sends packages on from there. It took quite a while to get to him and I received an email from him saying that the unit was not working. When I sent the unit it was in perfect working order. There is a little bit of a different turn on process with this amplifier as it has a power switch on the back that you turn on first, then you push the button on the front panel which puts the unit into standby mode. You then push that same button again to get it going into warm up mode which takes 9 seconds. I have explained this to him and the buyer says it is still not working. I then sent the instructions which I found online at the manufacturers website to make sure he understands. I don't know if there is a language barrier or not but I asked if the boxed was damaged and have not heard anything back. I would assume the buyer would have notified me if it was damaged as soon as he got the amplifier. What would you folks do in my situation? I have perfect feedback as I would never try to scam anybody and I over describe whatever I sell...I also package everything as bombproof as possible. So if the unit was working and there is no damage to the package what would you do? Refund his money and hope I get the unit back? Thanks for your insights and opinions.