Double glazing is one of the few big home purchases still sold door-to-door with high-pressure tactics, which is exactly why people overpay. The defence is simple: know a fair per-window figure (around £650 for a fitted uPVC casement), get three written quotes, and refuse to sign on a discount that only lasts until the salesperson leaves. Run your spec through the quote quality auditor and you will spot an inflated number fast.
The sales tactics to watch for
The classic is the today-only discount. The salesperson quotes a high figure, makes a show of phoning the manager, and comes back with a big reduction that only stands if you sign tonight. It is theatre. The starting price was inflated precisely so the discount could be staged, and the real aim is to stop you getting comparison quotes. Watch too for large upfront deposits, free upgrades that just hide the margin, and vague specifications that make like-for-like comparison impossible.
If a price is only good for tonight, it was never a fair price. I have watched firms quote nine grand, then drop to five and a half when the customer reached for the door. That tells you the real price was five and a half all along.
Tom Bradley, FENSA-registered installer
Fair per-window benchmarks for 2026
Keep these numbers in your head and you will know an inflated quote when you see one. The table below is fully fitted, including removal, sealing and the certificate. Compare any quote against the row for your style and material. A standard ground-floor casement quoted at well over £1,000 in uPVC is a red flag worth questioning.
| Style | uPVC | Aluminium | Timber |
|---|---|---|---|
| Casement | £400–£1,000 | £540–£1,350 | £760–£1,900 |
| Sash | £700–£1,500 | £950–£2,030 | £1,330–£2,850 |
| Tilt & Turn | £500–£1,200 | £680–£1,620 | £950–£2,280 |
| Bay (per bay) | £1,100–£3,000 | £1,490–£4,050 | £2,090–£5,700 |
| Fixed | £220–£440 | £300–£590 | £420–£840 |
| French Doors | £1,100–£2,200 | £1,490–£2,970 | £2,090–£4,180 |
| Bifold Doors | £2,200–£5,500 | £2,970–£7,430 | £4,180–£10,450 |
Source: DGCC 2026 dataset, cross-checked against Checkatrade and StayWarm.
Why three quotes is the rule
Three independent quotes, all specified identically (same material, same glazing, same style), show you the genuine market range for your job. Two is not enough to spot an outlier; three makes both the inflated quote and the suspiciously cheap one obvious. Specify the work the same way each time so you are comparing like with like, and ask each firm to break out supply, fitting and the certificate. If you are unsure whether to buy the glass and pay a separate fitter, our supply-only versus fully fitted comparison sets out the trade-off.
Three quotes, same spec on each, and read them side by side at the kitchen table with nobody selling at you. That single habit saves people thousands. The firms that overcharge are banking on you not bothering.
Tom Bradley, FENSA-registered installer
Red flags in a quote
Beyond the price itself, watch for a clutch of warning signs: no FENSA or equivalent registration, a demand for a large deposit before any work, no clear written specification, a guarantee that is vague or not insurance-backed, and any pressure to decide on the spot. Any one of these is a reason to slow down. Cross-check the figure against the cost per window guide and you will quickly see whether the number is fair.
What to do before you sign
Collect three quotes, check each against the benchmarks above, confirm the installer is FENSA-registered, and read the specification line by line. Do not pay a large deposit, and do not let the visit end with your signature. Sleep on it. If a deal really is good today, it will still be good next week. When you are ready to sanity-check the figures, paste your quote into the quote quality auditor.
Frequently asked questions
Get at least three written quotes, check each against fair per-window benchmarks (around £650 for a fitted uPVC casement), and never sign on a today-only discount. A genuine price does not expire at the end of the visit.
A fitted A-rated uPVC casement is around £400 to £1,000, with £650 typical. A uPVC sash is £700 to £1,500. Aluminium adds roughly 30 to 40% and timber 60 to 110%. A quote well above these ranges for a standard window deserves a question.
To stop you getting comparison quotes. A large discount that vanishes if you do not sign tonight is a pressure tactic, not a deal. The starting price was almost always inflated so the discount could be staged. Take the time to compare.
At least three, from independent installers, all specified the same way (same material, glazing and style). Three quotes show you the real market range and make any outlier, high or suspiciously low, obvious.
Often yes. National firms carry higher marketing and sales-team costs, which feed into the price, and they tend to rely more on discounting tactics. A reputable local FENSA-registered installer is frequently better value for the same specification.
Watch for prices well above the benchmarks, today-only discounts, large upfront deposits, vague specifications, no FENSA or equivalent registration, and pressure to sign on the spot. Any one of these is a reason to slow down and compare.