pricing is part of the english culture we all want a bargain, like was said in buying a car, if your the seller you will always ask for more than you actually want because you know someone will want to haggle the price, they always do even if it is in mint condition and listed under the book price.
When it comes to people like pro sales men for window companies they work on commision, the higher they sell the product the more they earn, also by dropping a few £1000 off the price the customer thinks they are getting a great deal and will want to buy, when in reality they are just paying a premium that they probably could have got done cheaper if they contacted there local builder for a price.
I know from carpet cleaning you sometimes give a customer a price and they start with "too expensive" sometimes when its a small job its not worth lowering your prices but giving them alternatives of multiple room discounts or other savings, some you just have to say thats your price so thats thats, (in the nicest way possible)