It follows an incident in the Blyth area when a man knocked at the door of an elderly woman claiming to have cleaned her windows and asking to be paid.
The 84-year-old woman handed over £20 and when she waited for her change, the man ran off.
Sergeant Garry Neill, from Blyth Neighbourhood Team, said: “We would advise people to be on their guard to anyone who calls at the door unannounced.
“Most people who employ a window cleaner will know who they are and when they are likely to come and clean the windows. If someone turns up you do not know and says they have cleaned your windows without a prior agreement then they should not expect payment.
“We would advise people to be on their guard to cold callers, especially if they are offering to carry out work or claiming that they have already done so. If the visit is genuine then the caller won’t mind waiting while their credentials are checked out.”
Further crime prevention advice to help prevent people being a victim of bogus callers is available on the Northumbria Police website
Anyone with information about this incident is asked to contact Northumbria Police on 101 quoting reference 1091 of 040117 or Crimestoppers anonymously on 0800 555111.