How to check a window company before you buy

Most people check a window company by reading reviews, asking around and looking at work nearby. Do all three, but don’t stop there. Reviews show how it went for other people. Before you sign, check who will make, fit and answer for your windows, whether they can sign off the work, and what protects your money if the company closes.

None of these checks costs anything. This guide works with any supplier, including us.

In short: what matters most, in order

1. Who makes, fits and answers for your windows.
2. Whether the company is registered with a scheme that can sign off the work.
3. What Companies House shows about the company and its directors.
4. Reviews, recommendations and local work: useful, but an extra.

And don’t sign on the day. Jump to the ten questions to ask any window company

Why aren’t online reviews the best way to judge a window company?

Online reviews come from an unusual group of customers, people read them in an unusual way, and some of them are fake. Use a star rating as a useful extra, not a verdict.

Who writes reviews, and how people read them

Most customers whose job simply went well never post a review. The ones who do write tend to have had a very good or a very bad experience. So a review page shows you the two ends and misses the middle.

The reading goes wrong too. People give one bad review more weight than several good ones.

Ratings can also follow each other. In an experiment on a news website, published in the journal Science, comments given an early positive vote went on to collect more positive ratings. Review pages can snowball in the same way.

A review is a snapshot, too. One written the week the fitters leave can’t tell you how the windows work after a winter.

So a score tells you something, but not what you most need to know: what happens if your job goes wrong.

A star rating is a useful extra, not a verdict.

Stars are for sale

Fake reviews are a trade. Some firms sell them, and some reviews are written by software. Government research in 2023 estimated that 11 to 15% of reviews in three common online shopping categories were likely fake. It didn’t cover home improvement, so treat that as a warning, not a figure for window companies.

Since 6 April 2025, fake reviews have been banned in the UK. So have paid-for reviews that hide the payment. The ban also covers fake bad reviews, written to damage a business. Banned doesn’t mean gone.

Testimonials on a company’s own website count for less, too. The company chose them.

Who will make, fit and answer for your windows?

Ask who surveys, who makes, who fits and who you call if something goes wrong. When one company does all four, one company is responsible for all of it. When the work is split between firms, a problem can turn into an argument about whose fault it is.

Ask directly whether the fitters are the company’s own staff or subcontractors, meaning another firm hired to do the fitting. Subcontracting isn’t wrong in itself. Buying from separate firms can work well, as long as each firm’s responsibility is written down. But you should know who will be in your home, and who stands behind their work.

Perfect Crystal Windows (PCW) works the first way. PCW brings manufacturing, technical support, survey and installation under one accountable team. Our own installers fit the windows we supply, and we don’t use subcontractors. So on the work we’re contracted to do, we answer for both the product and the fitting.

Can they sign off the work? In England, replacement windows have to meet building regulations, national standards for building work. A company registered with a competent person scheme can certify its own work, and you get a certificate afterwards.

Six government-authorised schemes cover replacement windows. The government’s list of approved schemes for replacement windows names them. Otherwise a building control body, an independent checker, has to approve the work.

Don’t take a logo’s word for it. Each scheme must publish its registered installers on its own website, so check the company there. PCW is registered with FENSA, one of the six.

What protects your deposit and guarantee? The schemes must make sure homeowners have some financial protection. Ask whether the guarantee is backed by an insurer, and which one, and whether your deposit is protected if the company stops trading. Get both answers in writing.

FIGURE A. ONE TEAM FROM MANUFACTURING AND SURVEY TO INSTALLATION AND TECHNICAL SUPPORT.

What do reviews, recommendations and local work tell you?

Reviews, recommendations and local work, used properly, show how a company behaves when something goes wrong. That is worth more than the star rating.

Find the review page the company actually runs. Some review sites show a page for a business whether or not the business manages it. Reviews can pile up there with nobody at the company reading them.

So ask the company where it collects its reviews, and give that page the most weight. If a page has no replies from the company at all, it may not be one the company looks after. Read the others too, but read them knowing that.

Ask the people who recommend a firm. If a friend or neighbour suggests one, ask them specific questions. Was the final price the price on the quote? Did the fitters turn up when promised? Was anything left unfinished, and how did the company put it right?

Look at local work. Windows fitted a few years ago show you more than windows fitted last week. Look at the sealant line, the flexible seal between the frame and the wall, and at the finish inside.

Don’t be put off if a company won’t give you a past customer’s address. A careful company protects its customers’ privacy and won’t pass on their details without asking them first. Ask for photos of recent jobs instead.

What should make you walk away from a window company?

Walk away from pressure to sign on the day, a discount that ends tonight, a price that isn’t in writing, or a company that won’t answer your questions in writing.

A price that only lasts today leaves you no time to compare.

Before you sign, ask three things. Can you cancel? Until when? And would you lose any money?

Get the answers in writing. For windows made to your measurements, the usual 14-day right to cancel may not apply.

Paying part of the cost by credit card may give you extra protection if the company doesn’t deliver. Your card provider can tell you how it works.

If you already have several quotes, our guide on how to compare window quotes properly shows you how to put them side by side.

Is a small or new window company a risk?

A small or new window company can be a risk. It has less history to judge, and if it closes, its guarantee may go with it unless it’s insured. That doesn’t rule it out, but the checks in this guide matter more, not less.

Start with Companies House, the official register of UK companies. Searching it is free. Check that the legal name matches your quote, that the company is active and that its accounts are up to date. Look at its previous names, too.

Then look at the directors. A new company name doesn’t always mean new people. Companies House lists the other companies each director has been involved in, and whether those companies closed. If a director’s last window company closed, you want to know before you pay a deposit.

Next, ask where you can see the windows before you order. A showroom lets you open and close the exact product. If there is nowhere to see it, ask for a sample and photos of recent jobs.

A long history isn’t proof on its own, either. A company earns its record by answering for its work year after year, and that is what to check, whatever its size. If a small firm passes every check on this list, it can still be the right choice.

FIGURE B. FOUR CHECKS FOR ANY WINDOW COMPANY, WHATEVER ITS SIZE: THE REGISTER, THE DIRECTORS, A SHOWROOM AND ITS TRACK RECORD.

Checklist: ten questions to ask any window company

Does the company name on the quote match Companies House?
Which competent person scheme are you registered with, and can I check it on the scheme’s website?
Who will survey, make and fit my windows: your own staff or subcontractors?
If a measurement is wrong, who measured it and who pays?
Is the guarantee backed by an insurer, and which one?
After fitting, who do I call if something goes wrong?
Is my deposit protected if you stop trading?
Can I cancel after signing, until when, and what would it cost me?
Where can I see the windows you’d fit: a showroom, a sample or photos of recent jobs?
Will you put everything you’ve told me in writing?

Download checklist as a PDF

Perfect Crystal Windows has been manufacturing and installing for 25 years, with showrooms in London and Luton where you can see the windows before you order. You can look through photos and write-ups of our recent projects, and you’re welcome to put every question on this list to us.

Where these rules and findings come from

Signing off replacement windows (England): The Building Regulations 2010, Schedule 3, as amended, which lists replacement windows in an existing home as work a registered installer may self-certify. GOV.UK, Competent person scheme: current schemes and how schemes are authorised (updated 17 September 2026). GOV.UK, Competent person schemes: conditions of authorisation (April 2016), conditions 15 and 17.
Fake reviews (UK): Digital Markets, Competition and Consumers Act 2024, Schedule 20, paragraph 13, in force since 6 April 2025. Competition and Markets Authority, Fake reviews guidance (CMA208, April 2025).
Cancelling (UK): Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013, regulation 28(1)(b), on goods made to the consumer’s specifications.
Card protection (UK): Consumer Credit Act 1974, section 75.
Research on reviews: Hu, Pavlou and Zhang, MIS Quarterly (2017). Varga and Albuquerque, Journal of Marketing Research (2024). Muchnik, Aral and Taylor, Science (2013). Department for Business and Trade, Investigating the prevalence and impact of fake reviews (April 2023).