The Consumers' Institute says shoppers need to be wary of name brand goods being offered online at very low prices.
"If the price is very cheap then it's almost certainly a fake," said Institute chief executive David Russell.
He said sellers of fake branded goods were increasingly using the internet,
and he recommended buyers check the credentials of sellers before purchasing. Sellers with anything less than "perfect credentials" should be treated with caution.
The business manager of auction site Trade Me, Mike O'Donnell, said counterfeit goods had always been around and their presence had "risen proportionately" with the growth of the website.
Mr O'Donnell said Trade Me runs a "liaison programme" which currently includes 60 legally verified copyright holders working with Trade Me's investigations team to find fake items on the site.
Trade Me would remove an item if contacted by the copyright holder.
The programme aims to ensure that complaints are being laid by the right person, not just by a disgruntled or jealous trader.
Some consumers are already suspicious of brand name goods at bargain prices.
For example, a pair of "Chloe Paddington" boots, the "must-have" boots for the season, was offered for sale on Trade Me this week. Although they normally sell for US$995/pair in retail shops and are difficult to find in New Zealand, the bidding had only reached $225 by yesterday afternoon.
In the question-and-answer section of the auction, a potential buyer asked, "Are these 3, 5 or 7 star replicas?"
The seller's reply: "I'm not sure - I believe these are authentic - if not they are amazing replicas because I can't tell the difference and I'm the harshest critic!!"
By this morning, however, the boots auction had been shut down.
"The copyright holder got in touch with us and we removed the auction," said Mr O'Donnell. "It is the perfect example of our liaison programme working."
Mr Russell said that if buyers found they had been sold a fake under the impression that it was genuine, they could seek reparation through either the Fair Trading Act or the Consumer Guarantees Act.
Sellers who advertise their goods as replicas fall under a different category and can be dealt with under copyright infringement.
"Fake watches are popular and a lot of people collect those," he said.
Mr O'Donnell said he hadn't noticed a "huge spiking up" of the problem but warned traders that Trade Me has a strict policy of "three strikes and you're out". Sellers with suspected counterfeit items are given three warnings before they have their profiles suspended from the site.
He said the recent sale of Trade Me to Fairfax would not affect the way it handles traders with counterfeit goods.
* Karen Tay is a journalism student at AUT University.
The Consumers' Institute says shoppers need to be wary of name brand goods being offered online at very low prices.
"If the price is very cheap then it's almost certainly a fake," said Institute chief executive David Russell.
He said sellers of fake branded goods were increasingly using the internet,
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