No matter how safely you use ladders and how good you are at judging situations, accidents are what they are. More often than not unforeseen. You cannot predict every situation, especially when other people are involved. I've had numerous customers over the years suddenly appear at windows trying to pay me out of upstairs windows. I've had animals suddenly leap up windows and on one occasion two stupid boys who thought it would be fun to try to tip me off the ladder by forcing the window open I was trying to clean.
As for customers not liking wfp, and insisting on trad, well they don't give a hoot about our safety. I was even told this by one of my customers when I made the switch. He was one of four that I lost straight off. They chose to go with a trad guy who two years ago fell off his ladder after a particularly wet night and broke his wrist. He never returned to work and three of the four came back to me and the fourth went with another wfper. She too had been very rude to me when I tried to explain the safety issues.