Police are advising householders to be on their guard after a spate of unsolicited phone calls offering damp-proofing work.
The warning was issued to residents in Littlehampton, Worthing, Lancing and Shoreham after complaints to police and trading standards.
Complaints were made about the activities of a company cold-calling consumers and offering free damp course surveys.
A Sussex Police spokesman said: "They send round a surveyor who, after using a damp meter, tells the customer a damp course treatment would be advisable.
"The customer then signs the agreement for work to be carried out for a fee, which has been up to £3,000.
"Workmen then arrive very quickly to carry out the work and collect the money."
He said the company seemed to be targeting older people.
John Baines, a crime prevention adviser, said: "If you are contacted by such a business, don't sign anything or hand over any money."
Anyone with information can call Sussex Police on 0845 6070999 or West Sussex trading standards on 01903 839749.
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