Another useless tip for you.
When I changed to wfp last December, I noticed one of the problems with windows were the snail trails, when I was trad it was easy to remove them.
I found wfp was a little more harder to remove them, at first I stood there and scrubbed the windows until the trails finally disappeared, this sometimes took ages to complete a window that was full of them.
I started to study my own method and found that after a wash with pure water the trail had not been removed completely, although once it dried there was no trace of the trail, but I was still not a happy chappie, knowing I had not removed these trails completely, I never knew if the customer could see later if the sun shone through the window, so I used to do the ducking and diving routine but still I couldn't be sure they would show up later after I had gone.
After spending the past few weeks of studying these trails, I discovered the fastest and easiest way to remove them completely.
Instead of scrubbing this way and that way, Take a look at the trail and note the direction of the trail travel, I used to spend time scrubbing across the whole width of the trail until I reached the end, until one day, I decided to try it in the opposite direction?
If the trail say runs from left to right (or right to left, for the funny ones amongst you) Take your brush and run your brush along the length of the trail a couple of times and you will find the trail disappears completely and with very little effort, don't ask me why this works I just know it does.