We are a building company telling you how to vet building companies, so read this with that in mind. Every point below is something you can check about us as easily as about anybody else, which is rather the point.
1. A large deposit up front
The biggest warning sign there is. A builder asking for 30 or 50 percent before anything happens either has cash flow problems or is planning to use your money to finish somebody else's job. Payments should be staged against milestones that have actually been reached.
2. A quote that is one number on one line
If it does not break down what is included, it is not a quote. It is a starting position, and everything not mentioned becomes a variation later. Ask for it itemised, with a programme and a payment schedule attached.
3. No mention of building control
Almost every extension, loft and garage conversion needs building regulations approval. If a builder does not raise it, either they do not intend to notify, which leaves you with unsigned off work that will surface when you sell, or they do not know it applies. Neither is good.
4. Cash only, or a discount for cash
A discount for paying cash usually means the work is not going through the books, which means no VAT receipt, no paper trail and no realistic prospect of recourse if something goes wrong in two years.
5. No insurance certificate
Ask to see public liability insurance and check the dates on it. Any legitimate firm will send it over without hesitating. If it takes three requests and it never arrives, you have your answer.
6. Reviews you cannot verify
Five perfect reviews all posted in the same week, from accounts with no other activity, are not reviews. Look for reviews spread over time from accounts with a history. Better still, ask to speak to a previous customer directly, and ask for one whose job had a problem, because how a builder handles the job that went wrong tells you far more than the ones that went right.
7. Photos that are not theirs
Depressingly common. Reverse image search a couple of portfolio photos. If they turn up on a supplier's website or another builder's site three counties away, walk away.
8. Pressure to decide today
Discounts that expire this week, a slot that has just come free, someone else interested in the dates. Building work is a decision worth a few days. Anyone rushing you is managing their cash flow, not your project.
9. No written contract and no named contact
You should know who is responsible, what is being built, what it costs, when it starts and when it finishes, all in writing, before anybody lifts a tool. If the answer to who is running this job changes every time you ask, nobody is.
What to actually do
- Get three quotes and compare them per square metre, not just on the total
- Ask every one of them how payments are staged
- Check Companies House for how long the company has traded and whether it files accounts
- Ask for the insurance certificate and read the dates
- Ask to speak to two previous customers, and ring them
- Never pay a large sum before work starts
If a builder gets awkward about any of that, you have learned something useful for the price of an awkward conversation.
Want a number for your own project?
The estimator gives you a real range in under a minute, built on 2026 Nottinghamshire rates.
Get An Instant Estimate