TradeMe is urging people not to disclose their mobile numbers publicly on a listing, after a complaint that a buyer was targeted, held at knifepoint and robbed last Sunday.
Police advised the online auction site yesterday afternoon after a buyer said they were assaulted last Sunday.
Detective Inspector Uraia Vakaruru said some people who recently picked up property they had bought off TradeMe were robbed or assaulted.
He said people picking up what they have bought online could be putting themselves into a dangerous situation by going alone.
Mr Vakaruru said several online sellers were currently before the courts.
TradeMe's head of health and safety John Duffy said they were assisting police, who were yet to make an arrest.
Mr Duffy said in this case, it seemed the buyer had left their cellphone number in the questions and answers part of a listing and made themselves a target.