You pay import duties and gst on top of that if the value of the goods exceeds AU$ 1000. Shipping or insurance costs are not part of that AU$ 1000 but they must be mentioned separately on the invoice, if not, you'll also have to pay fees over them. You will get a notification from customs clearance through Australia Post or the courier company that was used that they have a parcel and that you have to pay fees. After your payment, shipment is released. Its as simple as that. Import duties can get very expensive so maybe next time, order batches that stay under AU$ 1000 each.