If your parcel is a $2 item coming from China, consider yourself lucky if you receive it one way or another.  Australia Post is in no hurry to deliver items they lose money on and are very low priority.

If your Postie is on a walking beat he is allowed a maximum weight in his back pack and your delivery could be 'carded'.  If your Postie is on an electric or motorbike he too has similar but higher weight allowances.  If a Postie's run that day has a ton of small Chinese parcels, he can offload to the contractor for Post Office pick up.

If your item is sent from within Australia and over 250g it automatically goes to the contractor for delivery in a van.  That's why the postage cost is higher.  Priority is ALWAYS given to mail posted from within Australia.

Delivery carding is a secondary option for mail delivery and there is usually a good reason why this has happened.  Speak with your Postie in person if you can and ALWAYS keep them on side.  They know more about you than what you think...

If you want detailed answers to your problems please join the Australia Post Online Community Forum.