"When Mr McBride approached the counter with the alcohol, he was seen to almost stumble. At the counter, he swayed backwards and forwards excessively. This was not merely moving from one foot to the other. When compared with other patrons in the premises, his behaviour was noticeable," the authority said in assessing CCTV footage.
The video showed him dropping his change and fumbling with other possessions.
The cashier - who had worked as a checkout operator for nine years - said she did not notice any obvious drunk behaviour and could not smell alcohol on McBride's breath.
McBride was seen staggering out of the supermarket and driving away, hitting the kerb a couple more times before leaving the car park.
He was found by police a few minutes later at his home 2km away where he was trying to remove the keys from the ignition of the vehicle.
McBride was breath-tested and ultimately convicted of drink driving, having a reading of 1441 micrograms of alcohol per litre of breath - more than three-and-a-half times the then-limit of 400mcg.
Constable Simon Colbert had to help him out of his car and said "he reeked of alcohol and his eyes were bloodshot".
His evidence was that the person who sold him the beer could not have failed to notice those signs.
General Distributors' High Court appeal was based on five points of law in which it said the authority erred.
Lawyers for the company said there was insufficient evidence to support the finding that the checkout operator sold liquor to a person who was already intoxicated.
But Justice Woolford disagreed.
"I am ... of the view that there was ample evidence for the authority to make the findings, which it did."
It was also revealed at the original hearing that the supermarket staff members received inadequate training in assessing intoxication.
The company said that would be addressed.
Takapuna Countdown's licence to sell alcohol will be suspended for seven days from February 9.
The supermarket's employee, Paul Tu'ungafasi, who was supervising at the time, will have his general manager's certificate suspended for 30 days from February 16.
Police have celebrated the court victory, saying the ruling "sends a clear message to anyone that sells alcohol".
Waitemata district prevention manager Inspector Claire Humble said being unable to sell alcohol for a week would definitely be a significant financial cost to the supermarket and she hoped it sent ripples through the industry.
"A significant amount of the police's work involves alcohol-related incidents, so it's key that people who sell it adhere to the rules around its sale," she said.
Countdown general manager of operations, Robert Moffat, said he was disappointed with the decision.
"We serve more than 2.7 million people a week across the country and we take our responsibilities around selling beer and wine very seriously," he said.
"While we're disappointed with the decision, we are reviewing the judge's comments to fully understand the implications for our business.
"This outcome sets a precedent that everyone involved in selling alcoholic beverages, whether that's in a bar or in retail, should be aware of.
"There is a limited window in which to observe each customer in a supermarket environment; at Countdown we are committed to training our team to do the very best we can every time and meet our obligations under the law."
