Dazza,
Not long after we started window cleaning Wor Lass and I were heavily threatend by two idiots (father and son) who even intimated a threat towards our Little Un. They said they knew which school she went to! This was face-to-face outside a Tescos car park.
Of course I wanted to go 'Geordie' on them, but was restrained by Wor Lass, the thought of bricks through our window, and getting kicked all over the place; so we called the police who were okay, but it still put a real downer on us.
I think that was our worst month ever in window cleaning; we didn't leaflet; nor did we do much work, money was tight. We weren't scared, not really, it was just a real downer; what a crap job?! I must admit I did carry a 'tool' in my pouch after that for a while; couldn't sleep and wanted to take 'direct action' big style.
I/we got over it though. The window cleaner who threatened me doesn't clean windows anymore; I haven't seen him in years now (I'm pretty sure he's a 'druggie').
The rest of my local window cleaners are great; there's Ian_Giles, Squeaks, Tommo, John_H, another John, Matt and Ollie, Simon G, Terry P, and even though some of 'em don't like each other 'cos they've poached accounts from each other; we still all pretty much a friendly bunch, or at least maintain a professional 'stand off'.
Dazza, if you're new to window cleaning and an established window cleaner feels threatend; take it as a compliment.