You will find that new builds, or houses that have not been cleaned for a long time and have paint, mortar or labels still on them, will need to be cleaned using the good old traditional method of getting up a set of ladders (safely, which can still be done!!) and using your scrapers to remove the debris. WFP will not remove this type of dirt.
However, you cannot just ignore the problem and say it's the fault of the builders and they need to sort it out. These things happen all the time and as "WINDOW CLEANERS", you need to be able to CLEAN THE WINDOWS, not just wash them with a WFP system, as this will not satisfy any customer and they will soon look elsewhere for the job to be done properly.
This type of work still needs to be done by someone, if you refuse to do it then your reputation as a professional window cleaner suffers and the customer will look elsewhere.
We clean both traditionally and using WFP up to 60', and I can assure you that both methods are done in a safe manner.
We carry out many builders cleans, commercial cleans and domestic cleans. Each and every time we ascertain which is the best method of cleaning for each job. Don't be afraid of using ladders if the job justifies it.