A man who agreed to buy a laptop and an iPhone from a stranger in Northampton town centre ended up with a bag containing just two bottles of water.
The man met the stranger outside the Grosvenor Centre at 4.45pm on Saturday when he asked him for directions to the library.
After getting into a conversation, the stranger offered to sell the man a computer and a mobile phone.
After being shown a laptop in the car park behind Marks & Spencer, the man handed over several hundred pounds in return for a carrier bag. The stranger then ran away and got into a silver car.
When the man checked what was inside the bag, he found it was just two bottles of water.
The stranger is described as eastern European, about 6ft and stocky with short dark hair. He was clean shaven and wore a black jumper, navy jeans and black trainers.
The car he fled in was either a Vauxhall or a Skoda.
In light of the incident, officers have warned people to avoid buying things from strangers in the street.
Witnesses, or anyone with any information about this incident, can call Northamptonshire Police on 101. Alternatively, information can be given anonymously to Crimestoppers on 0800 555111