Consumer watchdogs on Teesside are warning residents of the risks of identity fraud after it emerged cold callers copied personal documents.
The warning from Hartlepool Council's trading standards team comes amid concerns about cold calls by representatives of mobile phone firms.
People who signed up were not given any documentation explaining their rights to cancel the contracts.
But some also allowed callers to photocopy bank details and passwords.
The team is now investigating whether the copied details could be used for identity fraud.
Michael Welsh, Hartlepool Council's principal trading standards officer, said: "I am seriously concerned when personal details are taken down, especially in this case when personal documentation has actually been copied.
"Also, the representatives did not provide written details regarding the consumer's rights to cancel, which is also very worrying.
"People should always be very wary if approached by any cold callers.
"We are trying to contact the company concerned to check if it is bona fide.
"In the meantime I would urge people not to give any details to people if they receive cold calls."
Householders in part of Leicestershire are being warned to be on their guard against pushy doorstep sellers.
Complaints have been made to police about the high-pressure sales tactics used by 'cold callers' in Melton Mowbray and Market Harborough.
Telephone sales callers have also prompted concerns where firms are trying to sell security alarms.
Officers are reminding people that it is up to them who they let into their homes and they can refuse.
Pc Brian Voss, crime reduction officer, said: "While there may not be anything illegal in the actions of doorstep sellers and the people cold calling from these kind of companies, the tactics of some can cause distress to the people they approach - especially the vulnerable or elderly.
"There are simple steps people can take to help if they find themselves under pressure from sales people and I urge people to think carefully before allowing strangers into their homes."