West Mercia Police and trading standards have carried out checks on workmen and door-to-door callers as part of Rogue Trader Day.
Det Insp Amanda Bolt said "older and vulnerable people" were most at risk and police hoped to raise awareness.
"Bogus callers will often switch from one type of deception to another, depending on the time of year and what area they are in," she added.
Offenders often pretended work needed doing when it did not, she said.
Police urged people to ask for identification and check with the company concerned if they had any doubts.
Rogue Trader Day is a national campaign involving the 42 forces across England and Wales.
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