I'm not convinced that a USP is necessary in window cleaning.
I'm an honest, "does what it says on the tin" window cleaner. I believe that is sufficient for most customers. For the few who want/need special treatment, I can do that if the job is big enough and profitable, otherwise I'll leave them to people who have gained marketing degrees.
If you look at this bloke's back posts, you see he makes a lot of sense. Let's all keep this game in perspective eh? It seems that some people would like to be all things to all men. The name of the game isn't who's got the most bits of paper, it's about customers and having enough of them. Then, when you have enough customers, service them well. The guys wo are doing well in this malarky seem to be the ones who work their business well. In most cases, without the whistles, bells and shiney things.
Only my opinion of course, not trying to put anyone's nose out of joint.