"We are receiving numerous reports of people being taken advantage of, usually when paying for goods they haven't viewed," she said. "Our advice is to never take a seller for their word, no matter how legitimate they may sound."
She advised researching to see if the pitch stacks up, and taking "some basic precautions" when buying online.
Potential buyers should insist on meeting in person, with company, to see the goods before completing the transaction, and should not deposit money into another person's account before receiving the item.
Police also urged learning more about the trader, with simple steps such as a "tap on a person's profile on the product listing page to see if you have any friends in common, their marketplace activity, and any ratings they may have received".
There was also a need to ensure friends and family, especially the more vulnerable, were protected, and to provide ongoing support and advice.