Motorists are being urged not to hand over cash to scammers following several incidents across the county.
Offenders have been flagging down vehicles near petrol stations and supermarket car parks, claiming they need money for fuel.
They either offer jewellery to secure a quick loan or try to persuade the victim to hand over money. However, the jewellery offered is fake and worthless and the scammers make off with the cash.
An 84-year-old man handed over £20 to a man outside Tesco in Milton, Cambridge, who claimed he needed the money for fuel at 4.30pm on Wednesday (October 24).
The following day (Thursday) a 67-year-old woman handed over £80 to a man claiming to have run out of petrol in Wisbech Road, Littleport.
Both victims were given jewellery which turned out to be worthless.
There have also been incidents reported in south Cambridgeshire.
Detective Constable Mark Beaven said: "We would urge people to be on their guard against this type of fraud and to never hand over cash in such circumstances.
"If you are approached by someone asking for money, report the matter to police on 101."
Anyone with any information should call police on 101 or Crimestoppers, anonymously, on 0800 555111.