Buyers are being cautioned after a sting by online auction site Trade Me caught out 75 suspected counterfeiters.
The traders, who claimed to be selling "labeled" goods, may be prosecuted under the Fair Trading Act.
The Commerce Commission says consumers need to be aware that if something seems too good to be true - it probably is.
Trade Me is warning that the economic crisis is likely to increase the motivation for people to rip others off.
The company says in the past, counterfeiters have enlisted foreign students to on-sell phony products and it expects that to continue.
It is vowing to monitor the situation and conduct further stings.
Trade Me is also warning that spear-fishing attempts, where personal and financial information is lifted from e-mails, are also likely to increase.