To be fair, the quotes are fairly similar - within 10% - so what, for me, is going to be the deciding factor? Price is always important, but provided the difference is within reasonable bounds, it probably won't be prime. That may vary with the kind product you are buying, so that if you were buying 100% product, like a DVD or a book, you may go for absolutely the lowest price, but the greater the labour or service element, the greater the possibility you might choose to pay more than the lowest price. Double glazing is not that different to carpets - most manufacturers use the same frames and components, but the quality of installation could make a significant difference to the finished job. So they need to be competitive within a range, but not necessarily the cheapest. In fact I might be somewhat suspicious that the cheapest would be cutting corners somewhere. Assuming that they all have similar costs, and buying around the same price, I might worry that their installers are being paid commensurate with their ability i.e. rubbish. In fact if one quote was much lower (or higher) they would be almost certainly summarily be dismissed.
If you assume an acceptable range of say 10%, that means that on a £5000 order, someone could be making £500 more profit than their competitors, with a happy customer. So what will swing the deal? Recommendations are a great substitute for knowing an expert personally. If they can show me testimonials, or give me details of previous installations (especially anything prestigious like Buckingham Palace) that shows me that they are proud of their work. I also find myself leaning towards the pitch that focuses on the little things they do better ("We don't do anything 100% better than our competitors - we do 100 things 1% better") - attention to details "we use the best hinges and locks". A guarantee and being part of a recognised trade association is reassuring - in fact the more they talk about quality and service the more I am put off those who only gave a price and a specification.
If anyone talked ONLY about price, then I'm afraid they wouldn't be doing business with me, because it would be a fair assumption that they only want to talk about their strong points - not their weaknesses. Most of us have the same thought processes when buying something as any other consumers, so try putting yourself in the consumer's shoes when looking at your business.
