You will never get the right answer for this question, some people will be ok with it, while others will quote "the day of rest.
I have knocked on a sunday and I got work on it as well, I also get phone calls from people looking for window cleaners on sundays.
its not as bad as 30 years ago, when all shops where closed, you will find that sundays is becoming a family day where they can sort out things like this as a family, I have knocked on doors in the week and the wife has said "I will have a word with hubby first" on sunday at least hubby is at home.
I think the difference is with window cleaning, you are not "selling a product" but "offering a service".