Global Athletes Pty Ltd is a large sports goods retailer. It purchases sweet spot badminton set rackets for $110 each from Sport Australia Pty Ltd, a large manufacturer of sports products. Sport Australia has an annual turnover of more than 30 Million and has an accruals basis accounting system. Global Athletes Pty Ltd plans to sell the badminton set rackets at a 200% mark-up to its customers. In January last year, it purchased 100 racquets. However, in April, it discovered that 10 of these racquets had design faults, and it returned them to the manufacturer and obtained a full refund. Explain the GST consequences of this arrangement for both parties.

(Please give the answer based on Australia law)