When soft washing a house, I apply the house wash mix everywhere, especially on the windows and once it is clean then rinse everything, especially a good rinse on the windows. It does a great job on the windows, especially if there is a lot of dirt, mold, mildew and algae on them.
I tell the homeowners up front that there might be some water spots as we have hard water in our area but if they want them professionally cleaned I don't offer that but I can recommend someone that can come out there but don't know what they charge. So far I have not had any say that they will need a window cleaner come out after I finished and the water spots that are sometimes there are not a huge issue so far.
I am sure that there will be some customers that will want the windows perfect and that is ok, I don't offer those services as they are hardly ever asked for and I have a great friend of many years that is a professional window cleaner that I will recommend if those opportunities happen.