Slough Borough Council's trading standards is issuing the warning after a resident challenged two men about them working for Scottish Power.
The men said they were checking a faulty electricity meter but once inside the house they asked to see electricity bills.
The resident became suspicious and questioned the men, who admitted they were there to try to sign them up to a change of electricity supplier. When challenged, they left in a hurry. This tactic is also a known method of distraction and theft.
Senior trading standards officer, Peter Adshead, said: "This tactic is known to be used by unscrupulous sales teams who are often paid on commission for the number of consumers they sign up. If anyone needs to see a meter, they should show proper identification and give the consumer a chance to verify their identity. The best thing to do is never let anyone in your house without an appointment. Legitimate companies will adhere to this."
Victims of this scam or anyone who is approached by sellers using this tactic, can report it to Consumer Direct on 08454 040506.