Answer:
You may not necessarily be required to receive the return of a product that has been damaged, used or installed. You should ensure that this is covered in your Sales Terms and Conditions and state explicitly that you will not receive for return products that have been damaged, used or installed. However, the consumer guarantees under Australian Consumer Law will still apply to these products and you may be required to repair the product or refund the consumer if the fault or damage was not caused by the consumer.