I have never knocked before starting in 10 years, on most we dont knock when we have finished either.
How do you collect if you don't at least knock on the door when you have finished?!
For many years I used to always knock first, but as has been repeatedely mentioned, it just gives the customer the option to say 'not today thank you'.
I no longer knock, we just get on with it...of course there are a few where you have to either knock first, call them on phone or text them, because of locked gates and other access issues.
Although it's off topic, the 'pound a minute' thing is spot on, if you want to earn at a reasonable rate then you really do have to be up around there somewhere.
My own criteria is a 'pound per minute worked' ie, the actual time it takes to clean the windows, not allowing for driving to and from, or setting up.
If you can get this right then you are just about on the money...you are not going to be earning 60 quid an hour or £480 a day! There are just to many other factors involved for that to happen.
Ian