Moving from single entry to double entry
Debit all Asset accounts, Credit all Liability accounts and then Credit Capital with the difference of A-L.
Paid ATO for GST Settlement of $1000
Debit: GST Clearing $1000
Credit: Bank $1000
Sales Return of inventory, selling price of $660 including GST (100% mark up on cost price)
Debit: Inventory $300, Sales $600, GST Clearing $60
Credit: Accounts Receivable $660, Cost of sales $300
Unearned revenue, that is now earned
Debit: Unearned revenue, Bank or A/C Rec, Cost of sales
Credit: Sales, GST Clearing, Inventory