Had an idea. When I was in car sales we used to use a technique going back and forth between the customer and the sales manager. It was to get the customer on your side against the manager. Then when the manager wouldn't give them what they wanted, the customer was tricked into thinking you had worked hard for them and it wasn't your fault that they wouldn't knock more money off. They Often went on to buy the car off you, even though it was cheaper elsewhere because you and they were on the same side. (It really worked, people are that easily tricked).
I thought maybe if we had a printed card at quote time with set prices for windows conservatories etc then just tallied up there number of windows and presented them with the card/sheet with the total. They would accept the price and you would say that was the companies pricing policy, sorry. could they be won over to you against the company (even if you are the company)? Would work best if you have logos/uniform etc.
It came into my head when a new customer gave me a tip and said 'don't tell the boss'. I am the boss, but in a uniform I could have been just a worker.
Thoughts? It would also look better than what I do at the moment, just walk around, scratch my chin, um and ar then say £x.
You could also put terms and conditions on the sheet and everything included in the service.