Avoid Rogue Double Glazing Installers

How to Spot & Avoid Rogue Installers: 5 Red Flags When Choosing a Window Company

Posted by | December 29, 2025

Choosing new windows and doors is a big investment, one that should improve your home’s comfort, security and value. But sadly, not every installer is trustworthy. Across the UK, there are still rogue traders cutting corners, overcharging or leaving homeowners with poor-quality work.

If you’re looking to choose a window installer in the UK, here are five clear red flags to watch for, plus practical tips on how to avoid rogue traders in Scotland and find the best window companies instead.

Red Flag 1: No Written Quotes or Contracts

If a company refuses to put their prices in writing, it’s a major warning sign. A professional installer will always provide a clear, itemised written quote and contract before work begins.

Tip: Compare at least 2-3 written quotes from different installers before making a decision.

Red Flag 2: No Insurance or Guarantees

Trusted companies carry public liability insurance and offer guarantees on both products and installation. If they don’t you could be left out of pocket if something goes wrong.

Tip: Always ask for proof of insurance and a guarantee in writing.

Red Flag 3: No Online Reviews or References

In today’s world, every reputable window company should have reviews on Google, Trustpilot or social media. If you can’t find any, or worse, only find negative ones, steer clear.

Tip: Ask to see recent customer references or even photos of completed projects in your area.

Red Flag 4: Pushy Sales Tactics

Rogue installers often use high-pressure sales, claiming a “limited-time offer” or insisting you sign on the spot. A genuine company will give you time and space to decide.

Tip: Walk away from anyone who won’t let you think it over. The best companies rely on reputation, not scare tactics.

Red Flag 5: No Accreditations or Memberships

In Scotland and across the UK, trusted installers are usually members of industry bodies such as:

  • FENSA (Fenestration Self-Assessment Scheme)

  • CERTASS

  • TrustMark

If they can’t prove accreditation, it’s a red flag.

Tip: Always check their credentials online. FENSA, for example, has a searchable database.

How to Find the Best Window Companies in Scotland

  • Check accreditations: Make sure they’re FENSA or CERTASS registered.

  • Look for guarantees: At least 10 years is standard for windows and doors.

  • Read reviews: Google, Facebook and independent review sites.

  • Ask about aftercare: Reliable companies will offer maintenance advice and support after installation.

  • Shop local: Established local installers are more likely to care about their reputation in the community.

FAQs

How do I check if a window company is FENSA registered?
Visit the official FENSA website and use their “Company Search” tool to confirm registration.

Do all installers in Scotland need to be FENSA registered?
Not necessarily but if they aren’t, they should have an equivalent certification (like CERTASS) to prove compliance with building regulations.

What guarantees should I expect?
Most reputable companies provide at least a 10-year guarantee on frames, glazing and installation.

What’s the safest way to pay for new windows?
Avoid cash-only deals. Pay by card or bank transfer and make sure you receive an invoice or receipt.

Protect Your Home with a Trusted Installer

Don’t let rogue traders put your investment at risk. By knowing the red flags and checking credentials, you can confidently choose one of the best window companies in Scotland.

At The UPVC Company, we’re proud have hundreds of happy customers, we provide high-quality windows and doors across Scotland.

Contact our accredited team today, or order online for the best quality windows and doors at guaranteed prices.