Southern police are calling for people to vigilant after a "significant increase'' in people using Facebook to rip-off unsuspecting consumers.
Senior Constable Darryn Buist, of the Otago Coastal Proactive Safety Team, said people were being scammed by users who advertised sometimes expensive items through Facebook with no intention of supplying the goods to the purchaser.
The sellers used an alias, either by giving a false name or an unregistered company to advertise the goods, Snr Const Buist said.
Often sellers communicated only through Facebook with the buyer, who was then asked to deposit cash or funds into an account without actually speaking to, or confirming the identity of, the person they were giving the money to.
Expensive iPhones or vehicle parts were the most frequent goods advertised and some purchases had been worth thousands of dollars, he said.
"Using sites that are not reputable to purchase goods can be risky, especially if you don't first verify the seller's identity.
"If you think about it, you wouldn't leave hundreds of dollars in your letterbox for someone you have never meet or seen, on a promise they may or may not return someday with your goods.
He recommended using reputable online auction websites which offered greater protection.
If consumers used "a non-reputable site'' like Facebook they should confirm the sellers identity before completing the sale.
"You can do this by asking the seller for their cell phone number and ringing them to confirm the purchase, as well as asking their full name.
"If it's a significant amount of money, have a bank cheque made out to their full name as this can only go into their named account and will prove the identity of the seller or their respective account if they scam you.
"If you suspect a seller may not be legitimate, do not complete the purchase and report the matter to your local police station.''