Drivers are being warned to be wary of a potential scam involving men claiming to have broken down and trying to get money for fuel.
There have been 11 reported incidents since 9 October in Herefordshire, south Shropshire and Worcestershire.
Motorists have been asked for cash so they can buy fuel or offered jewellery or watches in exchange for money.
The men involved were described as being eastern European or of Mediterranean extraction, police said.
They were often seen with a dark BMW or silver saloon car, the West Mercia force added.
Acting Det Sgt Neil Lippitt, of the Force Intelligence Bureau, said: "We have recently seen an increase in calls about these men selling jewellery at the roadside.
"In most incidents, motorists are flagged down and asked to buy jewellery in order for the seller to buy petrol to get home.
"The sellers can be persistent and persuasive and the jewellery is usually very cheap gold or polished metal and not worth the money paid."