Hope he's not in Melbourne city, I'm having issues with a dodgy contractor misdelivering parcels right now. The first one was eventually delivered correctly after being sent to and signed for at the wrong address, the second one is still missing so far. It's not really your issue (or my seller's issue) once it states delivered, that's all on Aus Post. I get prompter replies when I bother them on Twitter with my enquiry number than any other way, so I'd recommend your buyer do that if they drag their feet.