Frederic owns a bookstore in Collins Street, Melbourne. Frederic is registered for GST. His records for the quarter ending 30 June 2021 are as follows:

Cash Receipts	$
Gross Receipts from Book Sales	$77,000
Interest Income from Term Deposit	$1,200
Gross proceeds from Sale of Bookcase (See Note A)	$1,900
Cash Payments	$
Purchases of Books	$11,000
Purchase of Bookcase (See Note A)	$5,500
Commercial Rent paid for the bookstore	$11,000
Electricity paid for the bookstore	$1,500
Tea and Coffee Supplies for kitchenette in bookstore	$150

Additional Information

• A bookcase that was used in the bookstore was replaced in May 2021.
• Where applicable, figures are GST inclusive.
• Valid tax invoices are held for all relevant payments.
• Frederic accounts for GST on a cash basis and lodges quarterly business activity statements.
• Frederic employs two part time staff

Question 1) Explain why it is important that valid tax invoices be held for all relevant payments in details