Most businesses offer items for sale at low prices in order to attract customers to the business. This is a legitimate form of advertising.
However, a business will breach the bait advertising provisions of the Australian Consumer Law if it is not able to make available a reasonable quantity of the goods or services for a reasonable period of time at the low price.
What is 'reasonable' depends on the circumstances. For example, if the advertisement makes it clear the goods are available at the discount price 'today only', the business doesn't have to have sufficient stock of the goods the following day.