Consumer watchdogs are warning shoppers Black Friday sales are regularly embellished and misleading.
Consumer NZ said it was the time of year when retailers went to extra lengths to entice customers to "part with their hard-earned dollars".
Investigations found many big-box retailers played fast and loose with sale price comparisons, where recommended retail prices were inflated.
Consumer NZ said a Kenwood benchtop mixer at Farmers was being sold for $520 earlier this year, discounted down from its recommended retail price (RRP) of $730.
Retrospective checks on PriceSpy showed during the three months prior, it was being sold for $520 more often than the RRP.
The watchdog said at the same time, the same model could be bought full price at Moore Wilson's for $450, or for $500 at 100% Appliances.
Consumer NZ spokesperson Jessica Walker said savings advertised were rarely as good as they seemed.
"A sale must be a genuine opportunity for consumers to buy a product at a discounted price for a short period," Walker said.
"Price comparisons must be based on actual market prices - so if retailers compare the sale price to the recommended retail price but usually sell the product below the RRP, it's misleading."
PriceSpy allows consumers to choose a date range and particular store to track the price of a particular item.
PriceMe offers a similar service.
"Price tracking shows when a product goes on sale at one retailer, usually other retailers will soon follow suit," Walker said.
"It's worth noting some stores will price match competitors."
Consumer NZ said shoppers should do their research, ask for a better discount or be prepared to wait.
Australasian luggage retailer Strandbags was fined $780,000 in the Auckland District Court last week for running deceiving promotions between July 2018 and January 2020.
Black Friday is on 25 November.