I think it's pretty much irrelevant wether the glass you clean is domestic or commercial. It's the price v time ratio that counts. I have a mixture of all types of jobs, and commercial is not always the most lucrative.
I also know window cleaners who have not put up their commercial prices for 10 years or so because they are terrified of raising the issue with the customer, this also has the effect of locking out any other window cleaners, but they are foolishly loosing income so they can have this superior air of " commercial only"
Recently i quoted 40 quid for a job, the previous w/c who had done the job for years charged 6.50, small wonder he had the job for years.
A mixed bag of work is always better, it will keep through going through good times and bad.
cheers.