The Commerce Commission is warning shoppers about the perils of today's Boxing Day sales.

Cut price deals on Boxing Day need to be genuine and not just be made to look cheap, based on unfair comparisons.

Commerce Commission commissioner Anna Rawlings said the commission commonly sees an item discounted before Christmas from $100 to $75, and then offered at half price on Boxing Day for $50.

Consumers might be misled, thinking they are getting 50 percent off the price, when it has actually been knocked down to a lower figure.

The Commission is posting videos on You Tube and Facebook to make sure traders understand the law and do not breach it unknowingly.

The videos cover topics including gift cards, extended warranties, and refunds and returns for those unloved gifts.

Ms Rawlings said the first video contains a few simple but important tips about shopping from the convenience of your couch.

"Online shopping is a great way to avoid the Christmas madness but it can get messy. Our first tip is to check if your supplier can actually deliver your gifts in time for Christmas Day. We've also got tips about buying event tickets, and what to look for in the fine print when shopping online."

Breaches of the Fair Trading Act, and can lead to prosecutions.

Bike Barn was taken to Auckland District Court late last year and fined $800,000 for misleading pricing.

The company pleaded guilty.

Dud gift this Christmas? You may be able to exchange it, but the law doesn't entitle you to a cash refund. pic.twitter.com/UbJaJLw2kF

— Commerce Commission (@NZComCom) December 19, 2017

- RNZ