It will show delievered when it gets to his local Post Office - it hasnt reached there, or it has, and they havent scanned it.

Have you contacted the buyer and checked with them if they have gone to their post office and asked if its there?   With my buyers, half the time, the post office doesnt put a pick up notice in their inbox if the parcel is too big to fit.. that includes PO boxes. The buyer sits there wondering where the parcel is and its been sitting at their post office the whole time.

If he has, and its not there, open an investigation with Australia Post - you have the tracking number.  Because its so close to where its supposed to be, I bet they find it. Let the buyer know what youre doing and assure them youre onto it. If Aus post says its lost, then the buyer needs a refund (you are responsibile for it, even in the post).  If Aus post shows delivery, the buyer doesnt get a refund, and you will have to stick to your guns and probably show proof to Ebay/ Paypal.