Bargain hunting shoppers are being warned to do their research before hitting the malls for Boxing Day sales.

New research from price comparison website PriceSpy shows in 2022, 17 percent of products on its website increased in price on Boxing Day.

Ten percent were subjected to a fake sale, a strategy where retailers incrementally increase a product's price and then abruptly lower it, promoting a discount based on that inflated price. For instance, it might advertise a 50 percent discount from the previous day's price, but compared to the price from 30 days prior, the discount might only be 20 percent.

Massey University marketing professor Bodo Lang said taking 15 minutes to look at previous prices could save hundreds of dollars.

"That's a really important step to do before you go shopping and before you're in what's called 'the web of marketing,' when you're in the store and you're committed and a salesperson is talking to you. It's very important to do your research before so you know what is actually a good price and what is not a good price."

Lang said checking price comparison websites is always his first step.

"What these websites do is they show the cost for that particular model at a variety of retailers, which is really helpful. They also show a price history, so you know whether the price it is available for at that point in time is actually cheaper than the historical average, or whether it's been bumped up."

He said retailers adopt a range of sales techniques to lure in shoppers, some legitimate and some not.

"It might be 'up to 50 percent off' and so shoppers think, 'oh, this is great, there's a bargain to be had' and they go into the store and once they're in the store they discover that very few items, and maybe only very inexpensive items to begin with, have that large percentage off and really everything else is either full price or only has a very modest discount applied to it."

In PriceSpy's consumer survey, 54 percent of respondents said they intended to shop on 26 December.

The average amount New Zealanders plan to spend on the day this year is $840.40, down from $1203.30 in 2022 and $954.80 in 2021.

PriceSpy's analysis of last year's pricing patterns revealed 44 percent of the products experienced a price drop on Boxing Day.

Almost one in five products listed on the website were reduced by 10 percent or more, with the average discount being 21.33 percent.

New Zealand country manager Liisa Matinvesi-Bassett said it was evident that Boxing Day presented significant discount opportunities for consumers, so long as they conducted important pricing research to be sure that the item they were looking to buy was being sold at a worthwhile price.

This story was originally reported by Emma Stanford, senior reporter on RNZ News