It really bugs me when I hear stories like Spotless's.
Similar - but worse - has happened to myself.
I really can't understand this sort of mentality. If you do a good job and are a decent sort of chap, I doubt anyone would lose many customers to a new window cleaner. And those you lost probably wouldn't be worth having in the first place.
Leekson (a member here), canvassed part of my round a few months back and I didn't lose one customer. That's not a bad reflection on Leekson; but it is a nice compliment towards me.
Not long after that, via this forum, we arranged a time to meet up, so he could see how a Shurflo back-pack worked.
Hopefully, once Leekson has more work than he can handle, and someone asks him from an area I do to clean their windows, he'll point them in my direction.
Networking with other window cleaners is better than fighting with them.