The police and a telco association say Kiwis face risks when buying second-hand phones online during the holidays.
"Every year, around Christmas time, we see a lot of second-hand mobile phones flood on to the market, as people get given new devices for Christmas" says Geoff Thorn, chief executive of Telecommunications Users Forum (TCF).
"The majority of these devices are from genuine sellers, but it's also the time of year our members see an increase in the number of fraudulent devices coming on to the market.
"Even if you check the serial number to make sure it's not listed as stolen, there are no guarantees."
Auckland City Police Detective Senior Sergeant Bridget Doell said buying second-hand goods always comes with an element of risk.
"We know that it's common for criminals to sell items - that have been stolen through thefts and burglaries - online through community pages on websites such as Facebook. If someone is selling a new iPhone for a significantly cheaper price online, then clearly that is going to look suspicious. Remember the old adage, if it's too good to be true, then it probably is," Doell said.