It used to be an American-only affair.

The term Black Friday reportedly originated in the 1950s when factory workers would call in sick on the day after Thanksgiving, in order to have a four-day weekend.

Then Black Friday became a once-a year in-store shopping event, with crowds of shoppers choking up malls across America the day after Thanksgiving.

But in recent years US-based retailers have introduced Black Friday to other countries around the world.

Black Friday and Cyber Monday are now firmly entrenched in the Australian sales calendar, rivalling more traditional sale events such as Boxing Day.

The Australian Retailers Association (ARA) and Roy Morgan predict a record $5.4 billion will be spent in stores and online over the four days of Black Friday to Cyber Monday.

But consumer groups are warning customers to beware before they open their wallets.

A Choice survey found that almost all Australians (92 per cent) have heard of the Black Friday sales, with just over half (52 per cent) expressing an interest in buying something during this year's event.

Best deals for Aussie shoppers aren't always on Black Friday: Choice

Choice carried out a six-month investigation, tracking the price of four espresso machines across 13 retailers, to see when the products were at their cheapest. 

Although retailer prices fluctuated during Choice's investigation, it found that overall Black Friday didn't offer the best deals.

"Instead, we found cheaper, or similarly priced, options on various dates in the six months prior – up to 33 per cent cheaper in some instances," according to CHOICE editor Margaret Rafferty.

However, Choice also tracked six months of price fluctuations to determine when each item was most expensive.

"Compared to those prices, Black Friday was cheaper by up to 25 per cent," it said, recommending people check the prices across a range of different retailers.

Choice says that legally, retailers don't have to offer a refund or exchange if something's the wrong size or if a customer finds it cheaper elsewhere.

It also warns that not all products available for sale are safe, and that price doesn't equal performance.

"Particularly when it comes to appliances and tech, there's so much variation and choice on the market, it's easy to get duped into buying a dud," Ms Rafferty said.

The Australian Competition and Consumer Commission (ACCC) has also been tracking whether retailers are offering customers actual discounts.

In May online retailer Kogan Australia was sued by the consumer watchdog for offering fake discounts to its customers.

UK consumer group gives tips to avoid getting a dud deal

UK-based consumer group "Which?" also carried out an investigation into Black Friday sales.

It found that for UK shoppers, more than 90 per cent of Black Friday deals were the same price or cheaper in the six months before the sales event last year.

The consumer association told shoppers to make sure the discounts were "truly genuine" ahead of this year's sales.

It analysed items by looking at the prices offered by six companies every day during the six months before and after 2020's Black Friday, as well as on the day itself.

It found that 184 out of 201 items from six retailers, which included Amazon, AO, Argos, Currys, John Lewis and Richer Sounds, were priced the same or cheaper before Black Friday in 2020.

Which? suggests that before shoppers rush into impulse-buying a discounted product, that they check the price of the product across multiple websites and any footnotes about the offer.

It said retailers often highlight savings in red "as a way of influencing customers and they can be quite misleading".

"When we looked at items on special offer across major retailers for the first half of 2020, we found that several products were listed at their lower price for longer than they were at their full 'was' price," it said.

"We've also found retailers using old RRPs (recommended retail prices) as 'was' prices, so they reflect the value of the item when it was first released, not its current value.

"Rather than automatically trusting anchor prices, it's better to check against other shops' prices to try to work out the true value of the item you're buying."

The consumer group also suggests looking out for notes or signs explaining offers, noting that "rules that govern special offers are vague".

"We've seen notes that explained the product was actually only at the higher price for a fortnight, six months before the current offer," it said.

In response to the Which? investigation, which was reported by British media, Amazon told the BBC that it sought to "offer our customers great value thanks to low prices all year round" and that customers could "easily compare prices, allowing them to make an informed purchase decision".

'Sales frenzy' tipped for Black Friday, Cyber Monday, but supply shortages loom

Australian Retailers Association chief executive Paul Zahra tipped a "sales frenzy" over the Black Friday and Cyber Monday shopping period.

"For the past two years, November has beaten December as the biggest month for Australian retail sales throughout the year.

"Black Friday and Cyber Monday can be credited with this trend as people snap up some bargains and shop early for Christmas."

But he warned consumers to be prepared for delays on their product arriving due to supply chain issues.

"With our supply chains under significant pressure, consumers need to be shopping early if they want their products to arrive in time for Christmas," he said.

"There are several issues that retailers are navigating at the moment — everything from COVID impacts, shipping delays and threats of industrial action from port workers and delivery drivers. There's a perfect storm of issues so consumers need to get in quick to ensure they get the products they want."

Choice says while better discounts can be found at other times of the year, if it's an item you are desperate for, it may still be worth adding that item to cart on Black Friday before it becomes unavailable due to supply shortages.

"Our investigation also found that, over time, several stores no longer carried the item in stock," Ms Rafferty said.

"This is typical of the appliance cycle – as products get older, they're often replaced with newer versions from the manufacturer."