The CCTV shot shows the woman the police are seeking.
A thief who dashed out of a jewellery store wearing a $13,000 sapphire ring yelled "thank you very much" to staff as she ran to her getaway car.
Police are trying to find the woman and have released CCTV footage of the incident that clearly shows her in the store.
At 11am last Thursday, the woman went into Nuttall Jewellers in Birkenhead.
She peered into the glass display cases, checking out expensive diamond rings before asking staff if she could try on a sapphire ring that was in the window.
The ring had about 13 carats of sapphires set on an 18-carat gold band and was worth $13,000.
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Store manager Savita Mistry said that after the woman, who had been in the store just eight minutes, had put on the ring she asked to try on a ruby ring.
"She said she wanted to see how the ruby looked like against her skin. The sales person said no, we only allow people to try on one ring at a time," Ms Mistry said.
"Then she just said, 'Thank you very much', and ran out of the door with the ring on her finger."
The footage shows the woman taking the opportunity to leave while the saleswoman is behind the counter.
Staff chased her and saw her get into a white car.
"It was a couple of parks along from the store, it was unlocked. She got into it and drove away," Ms Mistry said.
"We tried to get the number plate but she had a flag covering it. We could only see the first letter and it was a C.
"She had obviously planned this very well."
The police were called and given the store's security tapes. Constable Brad Sanderson said it was a very brazen theft.
"We're very keen to hear from anyone who can identify this woman," he said.
Ms Mistry said the ring was insured, but as the excess was high and a claim would affect the policy premium, she would not be pursuing the loss.
The store has been robbed twice in the past.
• November 2012: Thieves armed with hammers smashed the windows at Partridge Jewellers in Newmarket, stealing 30 top-of-the line Rolex watches.
• March 2004: An armed robber stole tens of thousands of dollars of jewellery from Walker & Hall Jewellers on Broadway, Newmarket. The man entered the store with a knife and ordered two staff and two customers to the back of the shop before demanding rings, earrings and a box containing cash be handed over.
• June 2001: Four men ran into an open Queen St jewellery store and used iron bars to smash display cases before grabbing hundreds of thousands of dollars worth of jewellery.
The 19-year-old was in the first of many surgeries, her mum said.