Screening out cowboys and finding someone good are different exercises, and most advice only does the first. A red-flag checklist tells you who to walk away from. It says nothing about which of three plausible, insured, well-reviewed builders will do a good job on your house. That needs positive evidence, and there are four places to find it: the quote, the references, the contract and the way the builder talks to you before any money changes hands.
The quote is the first work sample you get
A quote is the only piece of a builder's output you see before committing, and it is more informative than it looks.
A good one separates labour from materials, which the FMB specifically recommends asking for. It states whether VAT is included. It names the products and specifications rather than describing them generically. It identifies the exclusions rather than leaving them to arrive later: skip hire, scaffolding, parking suspensions, specialist trades. And it carries a provisional sum for the things nobody can see yet, such as the state of the joists under a floor.
A quote with none of that is not necessarily dishonest. It is evidence about how the job will be run, because a builder who will not itemise a quote will not itemise a variation either.
Citizens Advice uses the words this way: a quote means a fixed price, so you know what you are getting and what it will cost, while an estimate is not the same thing. That is trade convention rather than law. No statute defines either term, so the label on the document settles nothing on its own. The two words are used interchangeably by people who ought to know better. Ask which one you have been given, and then ask for the figure and what it covers in writing, because that is what binds.
References you can visit
Ask for addresses rather than testimonials, and ask for jobs of the same kind as yours: a rear extension on a Victorian terrace rather than a new-build bathroom.
Ask for a job finished two or three years ago as well as a recent one. Building work looks good on handover day almost regardless of quality. What separates a good builder from an adequate one shows up after two winters: whether the render has crazed, whether the flat roof still holds, whether the new brickwork has moved against the old.
The question worth asking a past client is not whether they were happy. It is what went wrong and how the builder handled it. Every job of any size has a problem; the answer tells you about the builder's conduct under pressure, which is the thing you are buying.
Verify the accreditation rather than admiring the logo
Citizens Advice is specific: check whether the trader is a member of the scheme or trade association claimed, using that body's own published member list. Search the exact company name on the quote, because the legal entity and the name on the van often differ.
Membership of a vetted scheme is a signal rather than a guarantee, but it carries information. An FMB member has been through vetting on trading history, credit history and insurance, with independent inspection and regular re-inspection.
What a good builder says before you sign
The strongest signal in the whole process is a builder telling you something you did not want to hear.
Someone who says the timeline is optimistic, that the neighbour is likely to dissent under the Party Wall etc. Act 1996 and that you will be paying for two surveyors, that the joists may need replacing once the floor is up, or that you should add a contingency of at least 10% as the FMB advises, is managing your expectations before you are committed rather than after.
The opposite pattern is a builder who agrees with everything, quotes the shortest programme and the lowest price, and treats every complication as something to worry about later. Later is when you are paying for it.
The contract tells you how disputes will go
The FMB publishes a contract checklist, set out in the answer on what to check before hiring a builder, and a builder who works to something like it has thought about failure in advance. Rather than repeat the list, look at which parts they volunteer. Two clauses distinguish a serious builder more than the rest: a pre-agreed rate of liquidated damages if the job overruns, and a snagging agreement. Both are about what happens when things do not go to plan, and a builder willing to sign up to them in advance is telling you something about their confidence.
Communication is a competence, not a courtesy
Notice how the pre-contract phase runs. Whether calls are returned, whether the quote arrives when promised, whether questions get answered clearly. This is the best behaviour you will ever see from that firm, and it sets the ceiling for what happens when the job is under strain.
Good builders are found by checking rather than by instinct.