the guy who does our house left us a slip with a basic pictures of a window i.e single, double, treble, bay etc with a price under each one, and basically invited us to quote our own house. All the prices were the same, but it saved any confusion.
Just out of curiosity, i walked round the house and priced it, and he does it for that price.
seems like a decent idea, at least the customer knows what he's in for without the feeling of being pressured. Also, you can't be accused of undercutting because nobody has told you what they are already paying.