We have had a recent report of cold callers offering to do drive and roofing work. They provide glossy leaflets and have a van with a company name painted on it.
However, residents who have employed them report shoddy work and demands for payment far in excess of the price quoted initially. When challenged, they have become very intimidating and threatening, forcing people to pay up despite their better judgement.
Our advice is never to engage workers who contact you unannounced. Experience shows that the work is rarely value for money and, because you cannot contact them, you have little redress.
If you want work done, get several quotes from reputable tradesmen whom you have chosen yourself.