The down side of this job for me is the lack of mental stimulus. I'm going brain dead; is it an age related thing or a lack of mental stimulus?
 I must say, after some time I tend to get bored out of my tree on this job. Fortunately I live on a farm and come do some alternative work if I want. I’m very lucky really. Last year I went on a tree 
felling course coz I do some chainsaw work. Got all my felling certifications. And I felt very fresh going back to work on the windows. 
Generally speaking, window cleaning as a job is relatively stress free because you , as it’s your business ,can control different factors like bad customers and payers. 
Like Vin said earlier, you can build up your equipment for back up. 
Yes , you can fret about bad payers or you can deal with it, wether it be chasing it up or after a certain amount of tries , just writing it off. After all, it’s our time being wasted after each attempt to recover the money . What will an hour of your time cost you??
 The people commenting about their families ill health are the ones I feel for. I’ve been there. 
To go to work and come back to a sick household where work begins again when you step through the door is very stressful. The stress from those situations can make you extremely irritable and short tempered. 
I hope their situations improve over time. Or, that they find good solid customers.