as correct as the points you have made are, and a lot of them believe me are correct mate.
the point of your post is marketing, advertising is this way is not effective, (although the supermarkets do it all the time, they are more price wars) the reader is hit with loads of negatives, (what other window cleaners shouldn't be doing). it should not be about this, rather what you ARE doing, fill it with positives, we offer a monthly service, you CAN pay easily online or by check, we WILL clean all of your frames and be uniformed etc etc, i feel you will have a lot more success doing it his way, in fact why not leave what you have for a couple of weeks and then change it to the positive version and then see the return rates of each.
this is just my opinion judged by what i have learned from past experiences