An Auckland Council spokesman said it was accepted that Ms L'Estrange-Corbet was overcharged rates for the 2012-13 rating year. She would be refunded $3700 for that period of overpayment.
The designer bought the central Pitt St building for $875,000 with Francis Hooper in 2005.
"It has a category A heritage rating - the highest there is but has a limit on how you can change it," she said.
She found that restriction put off buyers when in April she put the building up for sale.
"I got an offer last week for $700,000. If Category A was not imposed by the council, it would be well worth $1.57 million plus ... ."
Ms L'Estrange-Corbet said she had to bring the brick building up to earthquake compliance at her own cost. An alternative, an approach to the council to buy the property from its heritage acquisition fund, was rebuffed.
A spokesman for Mayor Len Brown said he would meet Ms L'Estrange-Corbet next week to discuss her concerns.
John Church, general manager for the commercial and industrial division of Bayley's, said the revaluation of property values with earthquake compliance issues had created a totally new dynamic for the property sector over the past 18 months.
"Owners of buildings below the 68 per cent compliance rating are faced with the decision of whether to sell their asset at a value probably lower than it was in 2011, or invest in having the necessary engineering and strengthening undertaken to make their premises compliant."