Some exceptions were found for companies like tech giant Apple, which do not have much pricing competition in stores.
However the New Zealand Custom Service's $700 personal items limit could mean facing a $195 bill if buying duty free, so customers should check before making big purchases while travelling.
Wine was cheaper or comparatively priced at supermarkets or liquor stores.
You'd pay $7 more to buy a bottle of Brancott Estate sauvignon blanc at a duty-free branch than you would at Countdown, where it usually sells for $13.99.
"If you've got a particular product in mind, it's worth doing an internet search to see which price really constitutes a bargain, before heading to the airport," Chetwin said.
Consumer NZ's investigation found duty-free spirits, particularly liqueurs, were consistently cheaper.
But considering excise duty and GST often add up to half the price of a bottle of vodka, gin or whiskey, consumers might expect to save more than they actually did at duty-free.
On the day of Consumer NZ's price survey, a bottle of Jack Daniels - subject to $21 of alcohol duties and levies at the border - was only $5 cheaper duty-free.
"When you remove alcohol duty and GST from the sticker price, consumers might expect to see more significant savings when they shop duty-free than they get," Chetwin said.
The Commerce Commission warns businesses using the term "duty-free" to ensure customers are not being misled about pricing, something the Fair Trading Act prohibits.
It also advises duty-free stores to "clearly identify" goods not subject to duty.
Consumer NZ found nothing prominent alerting customers to this information in its investigation.
"Shoppers should be informed what is duty-free and what is not," Chetwin said.
The organisation is planning to lodge a complaint with the commission.
"The Fair Trading Act obliges duty-free stores to ensure their prices aren't at risk of misleading or deceiving their customers, whether they are from New Zealand or just in the country for a short holiday.
"While we encourage consumers to do their research before they buy duty-free, the ability of people to do this doesn't release duty-free businesses from their legal fair trading obligations."