The country's most prolific property speculators were banking $1000 a day in capital gains at the height of the housing boom, squeezing the most profit from poor neighbourhoods and centre-city apartments.
A Weekend Herald investigation into house trading found in the six years to 2018, the busiest professional operators were flipping more than 10 homes each, every year.
The 10 "top" flippers - most who conducted their business through registered property investment companies - held each property on average for just 70 days, and each netted a $70,000 profit.
Between them, they sold 750 homes over the six years analysed, making an estimated $50 million in gains.
Myma Copplestone, who flipped 63 properties with an average gain of $91,000 through her company MCK Enterprise, says although the numbers looked big on paper, after renovation costs and agent fees, sometimes she made as little as $8000 a sale.
"Renovation costs can blow out massively. And if the market is slow, like now, you have holding costs — you have to pay the mortgage all that time until you sell," she says.
However, not all of the properties were renovated - and of those that were, none of the sales checked by the Herald required building consents, meaning it was unlikely there were major additions.
OneRoof property commentator Ashley Church said the group of flippers who renovated were doing a public good by upgrading housing stock.
"But the second group, who just buy a property and sit on it for a few months and make a profit off the fact the market is rising - as far as I'm concerned that's a blight on society," he said.
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"They're not adding anything, just using it as an opportunity to make a dollar."
In total during the boom years, all speculators brought in $1.2 billion off flips - defined as residential properties bought-and-onsold within six months. There were more than 14,000 such sales nationwide.
Most of the activity was in Auckland, where central-city apartments (popular with foreign buyers) and houses in Manukau were hardest hit.
At flipping's peak in 2015, nearly one in 10 house sales in Manukau were by owners who held the property for less than six months. Nationwide, flipping was 4.6 per cent of all sales.
Data shows flipping plummeted alongside other investor activity as the market began to plateau in the past couple of years.
However, Auckland Council chief economist David Norman said despite some policy changes such as the foreign buyer ban and loan-to-value making property investment less attractive, without a wide-ranging capital gains tax it was likely once the market picked up again, flipping would too.