Agree with Vin on this one.
In our business people usually associate a low price with poor quality.
You don't have to go out and persuade people to convert to WFP. You are canvassing for new customers so you can provide a windowing cleaning service and earn a wage. Your side of the deal is to do a good job, be honest and reliable, polite and be respectful to them and of their privacy. Their responsibility is to pay you for the service you have provided.
How you provide that service is up to you and Health & Safety. The only objection that a customer can have with you using WFP is on old leaded windows if they leak water inside. It's up to you then if you will get your ladders out and do them by hand or not. If not then that is one house that needs a window cleaner but its not going to be you.
If the round you have purchased has been done traditionally then you need your friend to introduce you as the new window cleaner and you just turn up and clean them with your method. If your friend has just cleaned the glass only and left the frames filthy, then you have an easily convert but a harder job. People will love the clean windows, but getting them spotless will take time, especially if you have difficult windows.
Most customers know all about WFP - so just do it. You may have to explain to a few how the process works, but most of the time it goes right over their heads.
Practise on your own home and friend's homes first. Get the feel of your pole and get accustomed to using it, especially at an angle, ie window above a conservatory reached from the side of the conservatory etc.