When the unidentified man had approached the desk and asked if a black phone and credit card had been handed in, they were given to him without a check being made against Opatowski's clearly female name on the card.
Opatowski, a doctor, went straight to her bank and cancelled the card, but already $33 had been spent in a transaction at a nearby service station.
She is upset at the loss of the phone and the invasion of her privacy.
"I had some memories in the phone that I won't be able to recover."
A spokeswoman for the supermarket said it could have handled the situation differently and staff had been briefed on the proper processes to follow.
The spokeswoman said the phone was handed in by a trolley team member.
"Shortly after, a man in his late 20s/early 30's came to the customer service desk and asked if a phone had been handed in. He was very particular about the phone's appearance and that it had a card attached.
"This persuaded the staff member that it did indeed belong to him. The person was given the phone and card.
"Mrs Opatowski later came to the counter and asked whether a phone had been handed in – and sadly it had already been given to the person we know now to be a thief.
"The Pak'nSave team absolutely acknowledges that they could have handled this differently and have now briefed their staff on the correct process to follow e.g. requesting that someone provides additional ID or is able to 'unlock' a phone.
"The store has supplied the police with all the information they have at hand including CCTV to help them with their inquiries, and have also sought the assistance of other retailers and businesses in the mall."
Opatowski said a Pak'nSave representative had been in contact.
"The man was really nice. He said they really wanted to make things right. He offered an apology and said they want to reimburse me for my phone. I was really grateful."
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The phone was a One Plus that cost her about $700.
Opatowski has made a complaint to the police.
The police told the Herald they might not be able to respond to questions about the case until tomorrow.