You will not have to worry about it. The implemented model targets only vendors, to be as hassle-free for Australian customers as much as possible. It will be the vendor's job to determine whether it will need to charge you GST, and just like with local sellers, if it makes the wrong determination, any GST liability will be its liability, not yours.
Purchases from overseas over $1,000 will still be subject to customs importation rules as before.