The stall holder tried to open the box to check what was inside.
"I just said to her, 'I know what it is'. She said, '$2' so i handed over money and took it."
She posted a photo to the "Your Cats of Auckland" Facebook page, hoping that one of the 5000 members might be able to identify the wooden box, which had the name "Kaysha" engraved along with two paw prints.
Members recognised the box as distinctive to a local funeral and cremations business for pets in Penrose.
On learning of the woman's post, Pets@Rest general manager Mark Jagger confirmed the pet's cremation had been carried out at his business. He arranged to collect the box and tracked down the owner's son.
Jagger told the Herald that when the owner relocated to a retirement home, an estate clearance company was hired to clear out her property and the ashes were put out with the rubbish by mistake.
From there the box found its way to be on sale at Avondale Market, but just how remains a mystery.
The estate clearance company had the right to keep, sell or throw away whatever non-valuable items are found in a house, Jagger said.
The cat was cremated in November 2018. The owner's son - who did not want his mother identified - has asked the cremation company to discreetly scatter the ashes.