Buyer Beware:
Buying double glazing, the best and worst ways to pay for it 

This is an easy subject, because out of all the ways there are to fund any purchase, the best and worst ways are extreme opposites of each other:

The best way to pay for double glazing:
If you have sufficient spare money put aside, draw on this and pay for it outright, it is as simple as that. I say 'spare' because it is prudent to keep at least some ready money in reserve for emergencies and for any unexpected expense that could crop up.

The worst way to pay for double glazing:
The very worst way to pay for double glazing is on any form of finance, most particularly a finance deal offered by the replacement window-selling company. You can appreciate the true cost of finance if you multiply how much you have to pay a month by the amount of months over which the loan is spread, to get the total amount to repay. If you compare that total with the straight price, you will probably be horrified to discover that a loan over, say, five to 10 years could easily double the real the price of your purchase, or worse! The commission a salesperson could earn might be increased by 10%-20% by selling on finance, particularly if the finance was with the 'protected payment plan'. That is your money!

Middle ground:
If you do not have all of the money put aside or if you are not able or do not feel comfortable stretching yourself to pay for it all in one go, then consider asking a close relative to help you out with a loan. Offer regular payments over an agreeable period that you know you can honour, and offer to repay an extra amount over the top of that borrowed so that they will not lose out on their building society interest. That's fair all round! I also suggest a very simple letter of agreement.

On the other hand...
As for my comment about 'any form of finance', I fully understand that there are certain circumstances where getting finance to cover some or all of the expense is the only viable option. If this applies to you, than I suggest you visit Tesco or Sainsbury web sites and 'check out' (get it?) their very competitive deals or pick up a leaflet or ask at your own building society.

Getting a discount for paying CASH for your double glazing?
To a reputable concern whether you pay by cash or cheque should make no difference to the price. If you are asked for or you offer to pay cash in order to evade taxes then be warned, this is a very serious offence. We hear about the 'black economy', and anyone buying goods in this way is doing business with merchants who will be unlikely to give you good service and a proper guarantee. ‘No Income Tax - No VAT - No Comebacks - No Guarantee - We'll Cut Prices at a Stroke!’

Deposit guarantee:
If you are concerned about paying a deposit and maybe losing it if the firm goes bust before they have done any work for you, I suggest you go to someone else who asks for only a small deposit or no deposit at all. If you do part with a deposit then see if you can pay this using a credit card, as the card company will have a level of responsibility should it all go wrong.

Buying double glazing, final point:
Now I did say ‘any form of finance’ and meant just that, because it is you who will be paying back, somewhere in the price, the costs the supplier will incur of providing the ‘0% APR’ or the ‘buy now - pay nothing for xxx months’. Like all forms of advertising and special offers, these offers are all a ploy to lure you in and part you from your money. In my opinion the same applies to the purchase of a carpet, car or sofa. Go to someone not offering the special finance packages and you will get a much better deal.

My scam-exam test tells you far more about any individual estimate than my ‘buyer beware’ pages ever can because I have had to generalise very much on my website. Once you have put your estimate through the free test and had your results, you can then get an individual full five-page written report for a modest cost, and this should complete ALL the information you will need to be really clued in before you make any important decisions.

Further subject reading:
Can I believe the double glazing adverts?
Double-glazing salespeople - can I believe them? 
PVC-U double glazing quality and strength - the ONE most important thing to look for