Three people have been robbed at knifepoint this week after arranging to sell phones through a buy-and-sell social media page, sparking a police warning.
Canterbury police have responded to three similar robberies in the last week, with the third happening today.
Each time the "buyer" pulled a knife on the person trying to sell their mobile phone, before taking the phone and fleeing without paying.
In all three incidents the buyer and seller had arranged to meet in the Christchurch suburb Aranui around the Shortland Street area, at various times of the day, Detective Mike Kneebone said.
"We believe all three incidents are linked and are following strong lines of enquiry, but we're urging those buying or selling goods through unknown people, to act with caution," Kneebone said.
Kneebone advised both buyers and sellers to bring along a trusted companion, and to make the transaction in a public place in sight of CCTV cameras.
"Check who you are dealing with by searching for feedback and other comments relating to this seller to see what other people have experienced."
"Most importantly, if you're uncomfortable with the person you're doing the sale with, don't go through with the transaction."
Anyone with similar reports or information on these incidents is asked to contact Christchurch Central Police Station on 03 363 7400.
Information can also be provided anonymously at Crimestoppers on 0800 555 111.