He was working for insurance litigation firm Jones Fee, defending leaky building claims, when he saw his first leaky home.
It was 1999 and there was a feeling among defendants that the problem wasn't as big as the statements of claim were suggesting, he says.
"And I remember going with them as we took off a section of the wall and just seeing the damage.
"All the timber that was behind the cladding was black and you could pull it out with your hand.
"The only thing holding up the wall on this two-storey townhouse was the fibre-cement cladding on the outside and the Gib board on the inside. It was just amazing."
Several years later, Rainey stopped running defence against claimants to begin working on the side of building owners.
"I don't know too many people who got to law school with the ambition of acting for an insurance company and defending claims," he says.
"Most people get into law with the ambition that they will be there to help people and that they will fight for the underdog and champion their interests and fight the good fight."
Rainey's proudest moment came last year, when he travelled to Wellington to hear the Supreme Court issue its judgment in a case brought by Remuera couple John and Helen Osborne, disputing when the 10-year timeframe for bringing claims to the Weathertight Homes Tribunal kicked off.
The judgment concluded that the clock starts when a code compliance certificate is issued by a council, rather than when construction winds up.
Rainey says it was an issue he personally viewed as important enough to keeping pushing on with, despite rulings against him in the Weathertight Homes Tribunal, High Court and Court of Appeal.
"I believed that the argument that I was making was the right argument and it was the right way of looking at this particular statute," he says.
"A number of people have commented that other lawyers may have shrugged their shoulders and given up and walked away from it, but I kept going and we got the end result when it mattered and that is probably something I'll be proud of forever, I expect."
He established his own practice after parting ways with Grimshaw & Co, litigation lawyers who were at that time focused on leaky building issues.
Rainey says the desire to have a broader practice pushed him to go out on his own.
At that time he anticipated the number of leaky building cases would fall away by 2014, but now he sees another 10 years of leaky building litigation.
His most recent case was the $25.07 million win in April against Auckland Council and others over the faulty Nautilus apartment tower in Orewa - the largest payout to leaky building owners in New Zealand.
Other high-profile work has included representing a group of former Hanover investors, and having a management contract for Takapuna's Sentinel apartments ruled "harsh and unconscionable".
"We're very much a specialist litigation firm and that will remain our focus," says Rainey.
"That's the work I enjoy and the work I understand."
He says there has always been a focus on giving "110 per cent" regardless of whether it's a big corporate client or a small matter for a couple who own a leaky home.
So, has it all delivered the glamour he was hoping for?
"It has in a way that maybe I didn't expect it would."
Rainey says the financial rewards are probably not as high as people assume, so it's not as glamorous in that regard as some professions.
"But what it has really given me is every day I have an opportunity to come to work and do something that I care about and believe in.
"It gives me a chance to help people.
"Some of the great comments that we've had from clients over the years who have been grateful for our help and the work that we've done for them, I'll take that ahead of glamour any day of the week."
