I totally agree with Riz, if you are in this business and going around telling your customers that you get everything 100% perfect then you are either making no money as you are taking far too long on each clean or you are in experienced and have a bit to learn.
A great service and good quality clean is the best you can hope for not 100% perfect, there is a big difference, and that is the same which ever way you choose to clean windows or carry out any service for that matter.