I know that when I worked for a firm, you earn say £10 an hour, but don't realise you cost your company much much more than that to employ.
So I think people tend to imagine that if you make £20 in an hour, then you take home £20 an hour. Of course this is not the case. Overheads will eat into it down time due to weather etc.
It took me over a year to earn what I needed to when I set up 5 years ago. I used my savings during that time, and worked very hard to build my work.
Window cleaning, like any other trade can pay it's way, but you only get paid for what you do, unlike when you work at a firm where some get paid for turning up.
Not to worry a good stiff winter will show people the realities of working outside.