P @ F, if you've only been window cleaning for a year or so; you're doing fine.
Why not try and put your prices up, there's constantly threads here giving advice about how to do it.
I'm into my third year of window cleaning and put my prices up for the first time this year and it's made a huge difference. And remember; asking for a 'good' price is not 'sticking your kneck out'; as if you're being cheeky.
Ours is not an easy job. We don't get sick or holiday pay and we have expenses, tax and national insurance to pay. We can't work when it's too windy or dark.
Look at it from this point of view. Your customer's want a good, honest, reliable, insured window cleaner. Then they've got to pay for that service, and paying properly insures that they receive a good service.
There's customers around here that have had four different window cleaners in two years (me being the forth). (For the Chepstow lads reading this, they've been Ray, Tipper, Matt... then me).
I've been charging these new customers a 'fair' price, although more expensive than their previous window cleaners and each on has said yes, with only one exception.
So do your customers a favour and charge them a price that's fair on both of you. Then you won't be slogging your guts out for a low wage and they won't be complaining that you've dropped them in favour of better business.