In Australia there are certain requirements on how long a product must be at a price before you can advertise it as discounted, and say things like "save 50%".

In Australia there are certain requirements on how long a product must be at a price before you can advertise it as discounted, and say things like "save 50%". This is to prevent this exact practice where a store either lies and slaps a discount sticker on it without any discount to mislead a consumer, or from them putting up the price for 24 hours and then discounting it. There is no exact length of time, the law says "reasonable". So it'd be up to a court to decide. You can learn more here https://www.accc.gov.au/consumers/pricing/price-displays https://www.accc.gov.au/consumers/pricing/price-displays