Double glazing is a significant investment, and the industry has more than its fair share of high-pressure salespeople and misleading tactics. Avoid these five common mistakes and you’ll save thousands while getting a better result.
Mistake #1: Falling for the “Today Only” Discount
This is the oldest trick in the glazing industry. A salesperson sits in your kitchen, quotes £12,000 for your windows, then “calls their manager” to offer a “special” price of £7,000 – but only if you sign today. The truth is that the “discounted” price was the real price all along. The inflated quote exists purely to create urgency.
- Always get at least 3 written quotes from different companies
- Never sign on the day of the first visit
- If a price drops by more than 20% in the same meeting, the original quote was dishonest
Mistake #2: Choosing the Cheapest Quote Without Checking What’s Included
Not all quotes are like-for-like. A £4,000 quote might look cheaper than a £5,500 one, but when you dig into the details, the cheaper quote might use lower-spec glass (no Low-E coating), include no gasket or hardware warranty, skip the FENSA registration fee, use cheaper locking mechanisms, or exclude scaffolding and skip hire.
| Check This | Budget Quote | Quality Quote |
|---|---|---|
| Glass spec | Standard double glazed | Low-E, argon-filled, A-rated |
| Frame type | Basic 3-chamber uPVC | 5-chamber uPVC or aluminium |
| Hardware | Basic handles & locks | Secured by Design locks |
| FENSA certificate | Not mentioned | Included |
| Scaffolding | Extra £400 | Included |
| Guarantee | 5 years | 10–20 years (insurance-backed) |
Mistake #3: Not Checking the Installer’s Credentials
Any company can set up a website and claim to be experienced. Before you hand over a deposit, verify three things:
- FENSA registration – FENSA-registered installers can self-certify that work meets building regulations. Without this, YOU must pay for a separate building control inspection (£250–£400). Check at fensa.org.uk
- Insurance-backed guarantee (IBG) – if the company goes bust, an IBG protects your warranty. Without one, your 10-year guarantee is worthless if they close in year 3
- Reviews and track record – check Trustpilot, Google Reviews, and Checkatrade. Be wary of companies with fewer than 50 reviews or those under 2 years old
Mistake #4: Ignoring the Glass Specification
The glass makes a bigger difference to performance than the frame. Many buyers focus on frame colour and style but don’t ask about what’s between the panes. Here’s what to look for:
| Glass Feature | What It Does | Worth It? |
|---|---|---|
| Low-E coating | Reflects heat back into the room, improving insulation by 30–40% | ✅ Essential |
| Argon gas fill | Better insulator than air between panes, reduces U-value | ✅ Essential |
| Warm-edge spacer bar | Reduces condensation at the edges of the glass | ✅ Recommended |
| Acoustic laminate | Extra noise reduction for busy roads or flight paths | If near noise sources |
| Self-cleaning coating | Breaks down dirt with UV light and rain | Nice for hard-to-reach windows |
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Mistake #5: Paying Too Much Upfront
Reputable installers will ask for a deposit of 10–25% on order, with the balance due on completion. Be very cautious about any company that asks for more than 30% upfront or full payment before installation begins.
- Safe deposit range: 10–25% of the total quote
- Pay the balance: only after installation is complete and you’ve inspected the work
- Pay by credit card: for any purchase over £100, Section 75 of the Consumer Credit Act gives you extra protection
- Keep all paperwork: quote, contract, guarantee, FENSA certificate, and payment receipts
Bonus: Quick Checklist Before Signing
- ✅ Got 3+ written, itemised quotes
- ✅ Checked FENSA registration
- ✅ Confirmed insurance-backed guarantee
- ✅ Verified glass spec (Low-E, argon, warm-edge)
- ✅ Read recent online reviews (50+)
- ✅ Deposit is under 25%
- ✅ No pressure to sign today
- ✅ 14-day cooling-off period in contract
Frequently Asked Questions
Can I cancel a double glazing order?
Yes. If the salesperson visited your home (rather than you visiting a showroom), you have a 14-day cooling-off period under the Consumer Contracts Regulations 2013. This applies even if you signed a contract. Cancellation must be in writing.
Are national companies better than local installers?
Not necessarily. Large national companies often have higher overheads and commission-based salespeople, pushing prices up 30–50%. Local FENSA-registered installers frequently offer better value, more personal service, and the same product quality. The key is checking credentials, not company size.
Ready to Get Quotes?
Read our complete double glazing guide for everything you need to know before buying.