My biased opinion is that if you are getting paid to clean the glass, it better be perfect. The exception to that rule is if you and the customer agree to a somewhat "lesser" quality due to the fact that you are not actualy scraping with a blade and/or restoring with acids. You need to be sure that there is an understanding between you and the custy. If they want clean windows, they need to hire a window cleaning expert like ME - PaneLess Window Washing. (Shameless plugs are my specialty).
Don't get too cocky with your so called "clean" windows. Ya gotta see em from the inside when the sun is blazing through them at just the right angle. You'd be amazed and probably horrified to see what your clean glass looks like from the inside of the house and at the right time of the day - ouch!
My Water Fed Pole system for cleaning (outside only) windows cost me $3800 plus the pole which was $1250. The RO cartridge is nearly $1000 to replace about once per year, the DI cartridges run $99 each (2 of them) and the carbon prefilter is also about $100. I wish that I could make water with 0 Total Dissolved Solids for $.06 per gallon.
The use of the WFP system takes a fair amount of practice and the key to getting the glass spotless is to Rinse Rinse Rinse! Again, unless you are getting up onto the window to razor blade the entire surface of the glass, then you simply can't get em perfect.
My normal charge for scraping and squeegeeing a window is at least $9 per window (in/out + sills and tracks). Even then profit margins are slim. It's a ton of work even when you know what you're doing.
I'd bet that many of you guys do a pretty nice job on glass with your wands and with far less effort than me. Sometimes I wonder if I should take up pressure washing. I'm realy on this forum so that I can be the BEST window and roof cleaner that I can be!