DDP purchases of $300 or over are eligible for the TRS. You should read the following information carefully and ensure that you follow the guidelines. This has been copied from the Australian Customs site. Please go there for the latest information.
To claim a refund you must:
The refund only applies to goods you take with you as hand luggage or wear (unless aviation security measures, effective from 31 March 2007, in regard to liquids, aerosols and gels prevent you from doing so) onto the aircraft or ship when you leave Australia. It does not apply to services or goods consumed or partly consumed in Australia, such as wine, chocolate or perfume. However, unlike other tourist shopping schemes, most of the goods, such as clothing and cameras, can be used in Australia before departure.
The TRS is open to all overseas visitors and Australian residents, except operating air and sea crew.
The GST refund is calculated by dividing the total amount of the purchase by 11. The WET refund is 14.5 percent of the price paid for wine. For example, if you buy goods for a GST-inclusive price of $660 you will receive a refund of $60. If the $660 is made up of a camera ($460) and wine ($200), you will receive a total refund of $89 (total GST refund of $60 plus $29 WET refund on the wine).
For more information, go to the Australian Customs TRS site.