Start with the proportions, because they reframe the whole question. Citizens Advice logged 36,534 home maintenance and improvement complaints in the year to 30 June 2025, and low-quality services accounted for 52.8% of them against 14.3% for scams and rogue traders. Bad work by a real builder is roughly four times more common than outright villainy. The fuller breakdown sits in the answer on the most common contractor mistake.
That should change what you screen for. "Dodgy" conjures a stranger who takes a deposit and vanishes, and that person exists, but you are far likelier to meet a builder who turns up, works, invoices, and leaves you with something that does not hold water. Spotting the obvious cowboy is necessary and nowhere near sufficient.
The recognised red flags
Which? lists five, and Citizens Advice corroborates most of them. They are worth knowing precisely because the fraud case, though rarer, is the one you cannot recover from.
- A doorstep approach with no prior contact. Which? puts this first, and it remains the single most reliable signal: the entire transaction has been initiated by someone with something to sell about a problem you had not noticed.
- A large deposit demanded before work has started, or a discount for cash. Citizens Advice is blunt: avoid traders who only accept cash or want everything upfront.
- Vague business details. A mobile number and no registered address, no company number, no verifiable trading history.
- No accreditation, or a claimed accreditation that does not appear on the scheme's own member list.
- Poor paperwork. Unwilling to provide a written quote, a detailed contract or invoices.
Add one more that Which? flags separately: a trader who does not tell you about your cancellation rights. Traders working this way want to be in and out quickly, and the cancellation period is the thing most likely to stop them.
A discount for cash, on its own, evidences nothing. A sole trader under the £90,000 VAT registration threshold has no VAT to drop and is not being sinister by saying so. What matters is whether the price is conditional on there being no invoice, which is covered properly in the answer on paying cash for building work.
Pressure at the door is now a banned practice
The legal framing changed recently and most consumer pages have not caught up. The Consumer Protection from Unfair Trading Regulations 2008 were replaced by the unfair commercial practices provisions of the Digital Markets, Competition and Consumers Act 2024, which apply to commercial practices happening from 6 April 2025 onwards. Anything still citing the 2008 regulations is describing a regime that no longer operates.
The Act works on three levels. A general prohibition catches practices contrary to professional diligence that would distort the average consumer's decisions. Harassment, coercion and undue influence count as aggressive practices and are separately prohibited. And a schedule of practices is banned outright, in all circumstances, with no need to show that anyone was misled.
Two of those banned practices land directly on the doorstep trade: ignoring a request from a consumer to leave their home or not to return to it, and making persistent and unwanted solicitations. A builder who will not take no for an answer at your front door is not merely irritating. The conduct itself is unlawful, whatever the quality of the work being offered.
The enforcement change matters as much as the rules. Under the previous regime, action ran through the courts. The Competition and Markets Authority can now investigate suspected breaches and impose fines directly, which is why the DMCC Act is the frame to use whenever pressure selling comes up, on any trade.
If you have already agreed something
A contract forms far more easily than most people expect: verbally accepting a quote, agreeing a start date, paying a deposit or telling someone to go ahead. But an agreement reached in your home is an off-premises contract and carries a 14-day right to cancel, which extends dramatically if the trader never gave you written cancellation information. The full mechanics, including what happens when work has already started, are set out in the answer on how to tell a dodgy roofer; they apply identically to building work.
The practical point for builders is that the right survives the handshake. Agreeing something under pressure on a Tuesday afternoon is not the end of the matter, and a trader who wants you to believe otherwise is telling you which regime they are operating in.
The checks that filter
Given the complaint proportions, weight your effort towards competence rather than fraud.
Get three written quotes and read what each one excludes. Search the exact company name on any scheme register claimed, rather than trusting the logo. Ask for the public liability certificate and check the entity name and the policy dates on it. Ask for addresses of recent comparable jobs rather than testimonials, and go and look at one. Put part of the price on a credit card. Keep every document.
None of that is dramatic, which is rather the point.