Police have received calls from residents concerned about people knocking on doors in villages.
Places such as Bluntisham and Fenstanton have been targeted.
A spokesman for Cambridgeshire police said: “We’ve received calls concerning so-called ‘Nottingham Knockers’ across Huntingdonshire.
“These individuals will offer household goods for sale, at inflated prices, but often this sale is a ruse for checking out a person’s home.
“They may claim to be on a rehabilitation scheme trying to find work and may have a false trading permit or some other kind of official-looking identification.
“However, they are not part of any legitimate rehabilitation scheme.
“There is a Government-backed ‘Community Payback’ scheme for offenders who have been sentenced to carry out community work, but this does not involved door-to-door sales.
“Please be vigilant when answering your door and do not feel compelled to enter into any conversation with people if you do not wish to.
“If you have elderly friends, relatives or neighbours, it’s important to keep a look-out for them too and report any suspicious activity to police.”
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