if they dont want to agree to MY terms, then there is other window cleaners they can ask
You've probably got the right attitude, but what if they do ask another window cleaner whose got a more flexible approach to frequency? You may lose a good account for the sake of a two week increase in frequency and have another window cleaner in amongst some of your compact work?
It's probably more my insecurity, but when I'm bang on time for monthly work, my perception is that I am not wanted as frequently. As time ticks over I'm taking on more and more work, so as time goes on my frequencies are increasing; and I prefer that.
I like happy smiling customers, rather than, 'Is it that time already?' type customers.
I'm soft, I know I know.