Quite simply, anyone who is registered for GST is simply a tax collector working for the ATO!!
At the end of each month, quarter or year, the business owner has to work out how much GST that was charged out, and how much GST was collected – and the difference is then given to the ATO, or is claimed back from the ATO
If you’re not registered for GST then you cannot collect it, nor can you claim it back (It was never YOURS anyway)
If you are not registered or required to be registered for GST, you do not include GST in the price of your sales and you can’t claim credits for any GST included in the price of your purchases, even if they are for your business.
But if you can claim the expense as a personal income tax deduction, you can claim the entire expense, including GST, on your income tax return.