Building firms in Sussex are working to improve their image with the public.
Local members of the National Federation of Builders are working to drive the cowboys out of business.
They have issued a warning to householders and businesses to make a few checks before taking on building firms.
The warning comes after reports of sub-standard builders operating in Brighton falsely claiming to be part of the NFB.
Nationally, the NFB has 4,000 members with 120 based in Sussex.
Gary Amer, regional manager for the NFB in the South East, said: "Membership of the NFB is not automatic.
"Applicants have to meet stringent criteria proving their work and business is of a high standard.
"After the recent incidents in Sussex, people should be very cautious if they have doubts about the credentials of someone offering work."
Mike Wigmore, managing director of Sussex firm E A Chiverton, said: "I am amazed how often people undertake really quite major work without proper drawings and a clear estimate.
"It is tempting to think you are getting a bargain when someone offers to carry out the work for you for a much lower price.
"All it really means is they will have left something out which will result in trouble later."
The NFB has produced a number of free advice guides. For copies, call 0207 608 5160.
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