A gang of conmen is tricking people into thinking they are buying cheap laptop computers before handing over bags containing bottles of drink.
Police in Slough, Berkshire, say they have received a "steady stream" of reports from victims of the con.
In one recent incident, a woman handed over £400 in a car park to two men for a laptop and was given a case she later found to contain water bottles.
On 15 March, three people handed over more than £600 in separate incidents.
One victim was left empty-handed, one with a case containing a can of petrol and one with a bag containing two bottles of lemonade.
Thames Valley Police are warning people to be wary of those offering cut-price goods in the street.
A spokeswoman added: "We would also like to point out that buying property they know or suspect is stolen is an offence in itself.
"Not only that, but it creates a market that encourages robbery and theft."