A couple of things from the terms "The Prize cannot be exchanged, transferred, redeemed for cash or sold." (although i can not imagine how they could monitor a sale or transfer after it is in your possession lol)
I think this has more to do with you asking them to exchange the prize for something else you prefer, that they also have/sell, that may be of equivalent or lesser value. Nor can you ask them to transfer it to someone else (increases the liability for them), or ask for cash equivalent or sell it back to them. After you win the prize and have physical possession of it, they don't care what you do with it.
Note: you will be asked for your (Australian) Mobile number, and later will be sent a verification code to complete your entry.
You will also be asked how much you would spend on a pink diamond, with a variety of amounts (eg. 1000-1999)
A couple of things from the terms "The Prize cannot be exchanged, transferred, redeemed for cash or sold." (although i can not imagine how they could monitor a sale or transfer after it is in your possession lol)
"The Promoter collects personal information in order to conduct the promotion and may, for this purpose, disclose such information to third parties, including but not limited to agents, contractors, service providers and prize suppliers. Entry is conditional on providing this information. The Promoter may, for an indefinite period, unless otherwise advised, use the information for promotional, marketing, publicity, research and profiling purposes, including sending electronic messages or telephoning the entrant…."