"They're like a big, older brother," she said.
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"Whitcoulls are fantastic and what they don't have, they send everyone around here. They've always been open and good about it and sometimes people who don't know Unity end up being really good customers," she said.
Unity did not have enough room to stock a bigger range, but nor is it considering getting more floor-space for more stock.
"We have thought about expanding but we have an absolutely fabulous landlord who treats us wonderfully," McColl said.
Farmers and Whitcoulls owner James Pascoe Group said the decision to return Farmers to Queen St, to the building best known for its giant Santa at Christmas, was a result of "improved fashion and retail offering on Queen St".
Kevin Turner, the group's chief financial officer, said: "Whitcoulls will continue to retain a presence in the central city through our store located in the Downtown Mall."
He said the new Farmers would be open for business before Christmas, and that refitting would take place in the next couple of months.
Queen St has seen an influx of high-profile fashion brands in recent months, including TopShop and Prada. It has led to a revival of the street, which had been deserted by shoppers in favour of Westfield malls in the city's outlying suburbs.
The dominance of Amazon in the book-selling market has seen the collapse of previously strong book chains such as Borders and Whitcoulls in Auckland.
In addition to Unity, Real Groovy, at the upper end of Queen St, sells a wide selection books but it is first and foremost a record shop.
Whitcoulls in the Downtown Mall is a fraction of the size of the Queen St store and carries a limited selection.
Farmers used to have a presence on Queen St but the store closed in 2014 at the end of a long-term lease.
Farmers' chief executive Rod McDermott said that the Whitcoulls building lent itself to the department store. "The store will provide a full offering across beauty, fashion, lingerie, accessories and homewares," he said.
"There's no doubt it will continue to be a retail landmark in Auckland City, meeting the needs of CBD residents, the increasing number of travellers visiting the area and people who work or shop in the city."