Tbh I’ve never really gone overboard on the first clean I just look at what it’s gonna be worth to me long term,why lose it on the first clean when it might be worth 1500-2000 a year to you I’ve got many like that I do that needed a first clean and took a bit more time but long term are brilliant earners.
You can smell and time waster when you’ve been in this job for a while,I can’t see the point in ever charging double unless it’s a concrete sellotape or cement job,if it’s just a case that they haven’t had a window cleaner for years the old hot water gets em back clean.