Con artists are "laughing all the way to the bank" as they scam computer bargain-hunters in Sussex, police have warned.
Criminals make thousands of pounds by selling people empty containers when they think they are buying cheap electronic goods.
The trick reappeared in Sussex this week.
Police are urging members of the public to try to photograph people who contact them by their mobile phones, and take the number-plate of the scammers.
They are warning that even if a real sale is made, the goods are probably stolen, putting the customer on the wrong side of the law.
A man was walking in St Aubyns in Hove at around 2.30pm on Monday when two men in a blue car offered to sell him a Sony laptop.
He handed over £200 - but what he had actually bought was a laptop bag with two bottles of water weighing it down.
The driver was white, aged 35 to 40, with short, dark brown hair.
His front-seat passenger was aged between 50 and 60, and wearing a light-coloured T-shirt.
Another man called the police after he was approached in St Aubyns at around the same time.
Detective Chief Inspector Ian Pollard, of Sussex Police, said: "Yet again, we are hearing of an incident where people have handed over money for what they believe to be genuine goods, only to find out they have been cheated out of their money.
"It might sound harsh, but if people want to engage in back street transactions without stopping and asking themselves why the goods are being sold in this manner, then, in my opinion, they must have money to throw away.
"These conmen must be laughing all the way to the bank.
"It's quite simple - stick to proper retail outlets and you won't be conned.
"Being approached by complete strangers means one of two things: either you get nothing for your money or you are being offered stolen goods, which could actually result in you being prosecuted for handling stolen property.
"I'm sure most people think they would never fall for such a scam, but the fact of the matter is that they are. Use common sense.
"We don't want to hear any more reports of people who have been ripped off in this manner."
Anyone with any information can contact Sussex Police on 0845 6070999 quoting incident number 823:23:04:2007.
Have you been ripped off by a similar scheme? Leave your comments below.
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