You only have to worry about GST in Australia if you sell yourself. So if you sell over a table at cons/events, or you sell off your own website, you need to be aware of GST issues.
If you only get paid royalties from Amazon, Apple, Kobo etc., then you do NOT need to worry about GST. They do.
If you do sell yourself, the threshold for mandatory GST registration is Gross Sales of $75,000. At this point, you must be GST registered, which means you also must have an ABN (Australian Business Number).
If you sell under $75,000 gross a year, it is optional to be registered.
You pay GST on everything tax deduction claimable already. To claim it back, you must be registered for GST.
But the lower your gross income from sales, the less GST is involved, and for most authors, the actual amount of GST is insignificant, and you still get to claim it as a tax deduction.
The only reason to be GST registered is if you cross the threshold with sales you collect the money for, or you want to be, in order to claim GST paid back.
But before you decide you want to claim it back, consider how much record keeping and form filling this requires. Also consider, you can only claim GST back when you have a valid tax invoice from who you paid GST to. This includes the words "Tax Invoice" on the top, and an itemized amount of actual GST charged. Have a look at your next retail receipt, which conform to legislation requirements.
A lot of overseas organizations are doing GST totally wrong, and in fact illegally. For example, when you dont supply Facebook with an ABN (which has nothing at all to do with GST), they charge you 10% more. You dont get a tax invoice, and you cant claim this as GST paid, because it's a service charge, not the GST.
GST must always be INTERNAL to the price quoted, and everyone gets charged the same amount, from which GST gets paid to the government.
