Sarah, 58, estimates they have lost $500,000 since John, 62, first started going in 1996. Astonishingly, she estimates most of the money was lost in the past seven years when John was banned from SkyCity.
No one ever stopped him, even in the 18 months the couple spent in the VIP rooms where their identity was sometimes checked before entering.
Other times, she says, they were waved inside to enjoy the "free" drinks, food and hotel rooms that are the privilege of a valued customer.
It ended on April 27 last year when, for the first time, SkyCity matched the details it had collected in its guest book with John's details, which it had had on file since 2003. It flashed an alert, showing he was banned from SkyCity.
"You know you shouldn't be here," Sarah remembers the security guard saying as he escorted them out.
SkyCity says John was picked up when it began running the names of those collected at the entry to its "Eight" VIP suite through computers containing details of those banned.
The casino's corporate lawyer, Peter Treacy, says "we now have a system in place which requires all guests of our VIP customers to provide photo identification at entry to all VIP areas. The guests' details are then run through our databases to ensure they are not currently excluded."
The casino had held John's details since 2003 but last April was the first month it brought those together with its problem gambling records.
The change came at a time when a perfect storm around gambling was building, laying the ground for more decisions around the industry than New Zealand has seen for a decade.
SkyCity and the Government are close to a deal under which the company will build a $350 million convention centre in return for more gambling opportunities, 300 extra pokies and an extension to the casino's exclusive licence. Prime Minister John Key has promised society will have a chance to investigate the benefit and cost of accepting the offer.
The casino is already under scrutiny from the Gambling Commission, with its Host Responsibility Programme going through a review meant to have been held in 2009.
Looking after it clients, says Mr Treacy, is a responsibility SkyCity takes very seriously. "Providing safe entertainment for everyone is our top priority and we are continually investing in and improving our Host Responsibility Programme."
Parliament is also preparing to hear the outcome of the select committee examination of Maori Party MP Te Ururoa Flavell's bill to cut gambling harm. It would see a big restructuring of the pokie industry. And in Auckland, the Super City is mooting a policy which would see a sinking lid force down pokie numbers across a quarter of NZ's population.
"He never gambled," says Sarah of her husband. There was the occasional flutter on the horses, "but he was always mindful when he was putting money on a horse. You've got to walk up to someone and say, 'I'll have $2 on this'."
Sarah suffered a serious health incident in 1996, the year the casino opened. The couple's retail and service businesses fell into neglect as the pair struggled to deal with her recovery.
When the casino opened, John saw the possibility of relief - not just financial but also from the stress.
Sarah says: "That man walked in there and another man walked out and he hasn't been the same since."
The casino carried with it compulsive urges horses never had. And it was all pokies.
"You just take a $20 note and slip it in and your mind goes into snooze mode. It doesn't pay any attention to what you are doing. You're just pushing a button.
"Those machines can get hold of people and turn them into people that they never thought they could be before. It just about destroyed my husband. And he's a strong man. He's an intelligent man. It is his Achilles heel."
Some Fridays, he would go to the casino after work and return home on Sunday, spending 48 hours in the land where time stands still. There are no windows. "You lose track of whether it is day or night."
Sarah would go grocery shopping and not know if the Eftpos card would be declined. She began going with him to monitor his spending.
In 2003, she said: "'This is ruining the marriage. This is ruining your life. If you don't go and ban yourself, I'm leaving. I'll go with you and I'll ban myself as well.' I walked in and we banned ourselves. And we didn't go near it for two years."
The time passed and a month after the two-year ban lifted, John went again "to see if he was still addicted".
After months of losing himself to the casino again, a friend began expressing concerns, calling to report he had a problem. John was also aware he was out of control, and was banned once more.
The pull was impossible to resist, and one evening Sarah rang him to see why he had yet to return home from work. "I could hear the machines in the background." John admitted he was in the casino. "You're not meant to be in the casino," she told him. "They didn't stop me," he replied.
She rang SkyCity, reporting her banned husband and telling security which machines they would find him at. "They tapped him on the shoulder and escorted him out of there and put a trespass notice on him."
Two years passed until the order expired. This time, though, John needed SkyCity's permission to return. While he claims to have been unaware of this, the casino has records showing letters were sent to Sarah alerting her to conditions for entry. She says she never received them.
Sarah, who also says she believed he was allowed to return, began accompanying him.
She had a casino loyalty card, which records and rewards play, which he used. He denies it was an attempt to avoid scrutiny, saying it was just convenience for the couple to use just one card.
Their gaming escalated, as did their access in the casino. "We started with a red card, then purple, then to blue then gold and right up to the VIP lounge."
The VIP room is a social place. Eventually, security greeted them by their first names, waving them into the casino's most exclusive rooms.
"I didn't cook for 18 months," says Sarah. The casino would give them take-home meals which they would keep for when they weren't in there.
And it was social. The couple made friends and enjoyed a wide social circle.
She taught bar staff how to make her favourite Barbados Rum Punch. "They got really good at it too."
John stayed at the machines. In the VIP area, each spin of the wheel cost $1 or $2, so he preferred to play in the less-exclusive but still restricted Platinum Room, or more commonly on the main gaming floor.
"He would just keep pressing, pressing. I don't think it mattered to him whether he won or lost. It was the thrill of these machines and the noises going off in his head. And for an intelligent man, which he is, it is weird to think this could do it to him."
In a recent affidavit, a SkyCity manager testified: "The design of gambling machines is such that the longer a player wagers on a gaming machine the more likely they are to lose." They are geared to return 87 per cent of the money gambled.
John gambled so regularly he proved the statistical model. Sometimes he won. Mostly he lost.
"I remember him winning a $17,000 jackpot once. I think that was the only time he won anything substantial. More often than not he would be losing ... between $500 and $1000 a week.
"On one occasion he won and I thought, 'Wow, you've got $10,000 on you. We'll take that home'. And by the end of the weekend, he had $3000 left."
Sarah said she got bored. She would chat to friends, take walks around the city and just sit and watch. She saw people exchange huge rolls of $100 bills for "quick tickets" which could be fed into machines as if they were cash. When a gambler is finished, another ticket is spat back out again. She watched money being fed through the machines and out again. "There is no record of who has given that money. Nothing is signed for.
"If you were a drug dealer, you could say, 'I went to the casino and I won that money.' Someone could walk in there with $20,000, win a jackpot for $17,000 and say, 'I won it from a jackpot'."
One of the SkyCity's sought-after concessions is said to be TiTo - Ticket In, Ticket Out - machines which would make cashless gaming more common. Police have told SkyCity executives at meetings of concern money could be laundered through the casino using TiTo.
Sarah said she told security of other concerns but never heard what came of it. When Sarah and John did hear from SkyCity, it was to reinforce the value the casino placed on them.
"They would call us and say, 'How about a weekend?"' occasionally inviting the couple in to stay at the hotel as the casino's guests.
There was free valet parking. The drinks and meals. There were gifts. The electric wok, cooking scale. There were tickets to the cricket, the Blues and Breakers basketball. Often, they were hosted in corporate boxes.
Sarah was sure staff were aware of problems, with one saying to the couple once: "You've been here all night, time to go home."
She says: "In my opinion, most of the people who make it up to VIP are people who have a problem."
Australian research estimates casinos earn at least 30 per cent of their revenue from problem gamblers.
Submissions currently before the Gambling Commission call for greater external oversight of SkyCity's efforts. In contrast, the casino says it does all it can and is developing new techniques which will help detect problem gamblers.
Sarah: "I can see the harm of that place and I don't believe they are doing all that they can."
It ended on April 27. Sarah and John went to SkyCity. "You go on up to the eighth floor and you have to pass security. You flash them your [Premier VIP] card and if you don't have your card you have to show ID and sign in so they know who you are.
"After a while they knew us. Sometimes they would just wave us through."
On the last visit to the casino, there was a new staff member on the reception desk. The casino was front-page news, with the convention centre deal being scrutinised.
"They had a new guy on the desk that afternoon. I produced my [Premier VIP] card and John showed his driver's licence. This young guy thought he'd put us into the system."
They were waved through, not knowing the computer had shown John was banned.
"We would have our drinks and go and sit on the deck and have something to eat. This one afternoon, someone tapped [John] on the shoulder and said, 'You know you're not meant to be up here'."
Mr Treacy says the casino has "acted each time we have found this person on the premises" and does all it can to keep banned gamblers out.
"However, it is clear that some go to great lengths to evade staff. In addition to our own systems, we also rely on family and friends to act in the best interests of excluded patrons and help stop them from trying to return to SkyCity to gamble."
It gave John and Sarah a little extra help, after their case was raised with the casino. The couple gave the Herald permission to disclose their real names to the casino to allow it to respond to the allegations.
A few days later, Sarah received a letter saying she was also now banned. SkyCity sent it almost 11 months after asking the pair to leave.
Sarah and John are not the couple's real names.