Wonder sports is a large sports goods retailer. It purchases 'sweet spot' tennis racquets for $110 each from Aussie Tennis Goods, a large manufacturer of tennis products. Wonder sports plans to sell the tennis racquets 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 an obtained a full refund. Explain the GST consequences of this arrangement for both parties