The way Australia Post is these days, I am always checking on tracking to see if an item is on track (if you sell lots of items, it may not always be possible to be on top of this).  In the last week, I have had to open 2 "missing item" enquiries with Australia Post and when I do, I let the buyer know I am on to it ....... It's a way of heading off any bad feelings from the buyer in SOME cases - but I always make sure I respond with absolute courtesy if they do express 'bad feelings'.  Now this doesn't help in your particular case, after the event, but something to think of in the future.

I've had so many items delayed at Chullora NSW and other "Australia Post Facilities" and I see that your item got passed around a few 'facilities' in Sydney which is just unacceptable and unfortunately, uncontrollable !!

From reading these discussion boards, it all comes down to the "buyer's experience" which they reflect in feedback unfortunately, even if it is beyond out control.  Other members may have other advice for you in your particular case.