Read through this thread.
You've said "goods sold within Australia", but if the SELLER is overseas, it's an international purchase. It doesn't matter whether you purchased the goods on eBay.com.au or on eBay.com. It's where the SELLER/ITEM is located that dictates whether or not it is an international purchase.
The legislation came into effect in July 2018. Below is a quick overview from the thread to which I linked (which you should read in its entirety):
@countessalmirena wrote:
Information on GST for low value imported goods, contained in eBay's updated User Agreement:
17. GST on low value imports
From 1 July 2018, Australian Goods and Services Tax (GST) applies to the sale of low value goods (i.e. goods valued at AU $1,000 or less) imported by consumers into Australia.
eBay is considered an Electronic Distribution Platform (EDP) under the relevant legislation and therefore responsible for collecting the GST on low value imports and paying it to the Australian Government. This means that from 1 July 2018, eBay will add GST at checkout on all imports with an order value less than AU $1,000 and remit the GST to the Australian Taxation Office (ATO). We will not collect GST on orders over AU $1,000.
If you are a seller with products located outside Australia, you don't have to collect GST nor remit anything to the ATO in regards to your eBay sales. Any GST that applies for low value goods bought on eBay and imported into Australia is added to the order price and collected by eBay from buyers, then remitted directly to the ATO. You still receive payment for your orders as normal However, you acknowledge and agree that 1) your prices may appear 10% higher to buyers than before if their delivery address is in Australia; and 2) we won't report GST collected to you, although we will indicate on the order details page if GST was collected by eBay.
As a seller, you must not misrepresent the location of your items on eBay and you must comply with eBay's Selling practices policy. Sellers found in violation of this policy may be subject to listing removal, warnings and suspension by eBay.
If you are a buyer, you may see "GST may apply" when viewing items on eBay that are located overseas. You acknowledge and agree that if you buy a low value item on eBay from outside Australia, you will be charged 10% GST on top of the seller's item price (applied in your cart and at checkout). If there is any dispute as to the GST you have paid on an order, you should contact eBay. If you receive a full or partial refund for your purchase, you will also receive a refund for the proportionate amount of GST.
Our Tax policy contains more detail about when we charge GST on eBay. If you have any questions or require more information, please contact the Australian Taxation Office or seek independent tax advice.
In particular, the penultimate paragraph above should be helpful for eBay buyers wondering about how GST is managed with regard to refunds.
