I had an experience years ago not long after I started on my own, where my wife was asked by a family friend who used to have her windows cleaned by a mutual friend, actually the guy who originally started me off in window cleaning by teaching me and for a few months, employing me. She wanted me to clean her windows instead of him, as apparently, the quality of his work had deteriorated.
Now I had promised my windy friend that I would not canvass 'his' area. He was quite protective of his 'patch', but as I wasn't canvassing, reasoned to myself that I wasn't breaking my word. I went ahead and cleaned her windows, then her neighbours came out of the woodwork to ask me to clean theirs as well. Following the same principle, I obliged.
One day my windy friend drove along the street and saw me cleaning one of his erstwhile customers' houses. He was livid. I told him that they approached me, not the other way round, but it didn't placate him. For months he kept bringing it up, until eventually he packed up cleaning windows for a different venture.
My regret is that I didn't speak to him first. Had I done so, I am sure the situation could have been resolved in an amicable way.
John