How have you explained to your customers why you use the WFP and how it works?
Did you do it verbally, which is very difficult to get EVERY point across, or did you use David's WFP explanation letter from the documents to upload section?
Good communication is the key to a successful transition. Get it right and you'll have very few problem customers.
I numptyised a version of David's letter; it ended up into a 3 page essay on 'Why I'm using a WFP and how it works". I encouraged customers to read it.
Most did; a few didn't and those few who didn't and questioned me (why have you've left my windows wet?) I jokingly rebuked them for it, accusing them; saying, 'You didn't read my letter, did you?'
It put them on their back-foot straight away.
Then I explained it roughly and gave them another letter.
I honestly haven't lost one customer (though I thought I might) and I must've done over 1000 cleans with it by now.
Not only that, if the letter is well presented on good quality paper, looks good and is worded correctly; the customer will realise that you're not just another 'thicko school drop-out', which is their general impression of us 'window cleaning scallywags'.