Looks like a good old fashioned scam to me maggie !
Get as many quotes as you can, or as many as you can put-up with. ( there is a limit to how many reps we can allow in our houses, with their smart suits and even smarter talk )
Most double glazing reps are failed second-hand car salesmen. When I put in double glazing a few years ago, I chose a company that I thought was OK and I have no reason to doubt my decision. But a few days before they started work, one of the other reps I saw phoned me up and demanded to know why I didn't go with his company. When I told him who I DID go with, he said that he knew where that company got its glass from and threatened to make sure that company would give me "crap" glass instead of the best quality ! Unbelievable but true.
I ended the telephone conversation in a rapid and very Anglo-Saxon way. This rep by the way, was a recently retired South Wales Police Officer and I complained to the Company and the Chief Constable but I never heard anything further.
Double glazing is a business stuffed full of rogues, so watch your step !