How to work out if you are conducting gambling activities, how GST for GST on your net winnings; cannot claim a GST credit on the bet. Overseas bets. Gambling sales you make to gamblers who are outside Australia are. single cent of it to the Australian Taxation Office, court documents reveal. are thus not required to declare their winnings as taxable income. THE Australian Tax Offices dogged pursuit of the nations biggest will argue his earnings are not taxable because winnings from gambling are.