You can do, but technically you are supposed when door knocking to give your name - organisation - and purpose of visit as first sentence, if you had id that would be shown too- this is how we had to do it as sales reps for gas and electric firms, you can do it by just saying, "good evening my names sean, im calling on behalf of dolphin window cleaning, we are offering free quotes to save you money/do a better job etc,
I find people want to know who/why you are there pretty quick...
On the "dont offer quotes to people who have them already", make your own mind up about that as i dont feel personally theres a right/wrong answer, if you feel you are offering a better service, a more reasonable price not necessarily undercutting just for the sake, then its just business! Otherwise you are going to be stuck trying to find work, if the window cleaners in that area do there job properly you most likely wont take their work anyway, what i do is get to know the cleaners around me, and work out where is free, but work is work!!
Do this and you slow yourself up by 2 to 3 times , if you ask people straight off if they need a window cleaner then they know who you are , DONT BE AFRAID OF THE CANVASSING POLICE
