ID required when making purchases

My mum recently attempted to make a purchase on account at Sheet Street Newcastle Mall however the staff insisted on her producing her ID. This is an account she opened in her name and is only used by her. Since when did this become a requirement for shopping at Sheet Street and when wwre customers informed of this? Who moves around with their ID on them at all times? What's further baffling is that the they had my mum's new ID photo on their system already. Are Sheet Street's systems linked to Home Affairs? And again, when we're consumers informed of this or given the opportunity to object to the storage of their personal information?