It's all in the technique.
True, but there seem to be many different techniques on here, which makes things confusing.
Example (and I'm only on my second or third cleans since switching from trad):
Some people say scrub the frames, scrub the glass, then rinse an inch or two from the top of the glass - when I do this, there are small white spots across the top of the glass where I hadn't rinsed.
Others says rinse from the top frame all the way down the glass - I tried this and got a dirty streak down the middle of the window! So I get home and try this method on my own windows and they are spotless.
When I first started trad, I had some OJT for maybe 10 days and off I went. Something similar for wfp must be recommended, especially as you can't see the results of the upstairs cleans. I'm only earning with wfp what I was earning trad, and with a seemingly inferior finish on the glass (but the frames look great!) so it's very frustrating.