This was my take it or leave it email ... not worded smoothly but it did the job
Hi XXXXXXXX
Like all businesses from time to time we review our prices as we only have so many hours per day to create our turnover.
Since we started cleaning your windows back in early 2013 the demand for our services have increased dramatically and now it’s at a level where we can no longer service all of our customers unless we are achieving a turnover rate per hour that is achievable with our other work.
Unfortunately this means that we will no longer be able to clean the windows at XXXXXX XXXXX at the current price of £90.
To bring your price up to our current levels would see a required increase of £120 making a new price of £210.
Obviously in percentage terms this is a huge increase - however it reflects, that in May 2013 I under-priced the job but have stuck to my price for over 2 years whilst I could afford to, it brings it in line with what we charge our other customers and means no further price increases for at least 2 years.
You may like to seek another quote and possibly go with another window cleaning company ( obviously I hope not) so I will wait to hear confirmation from you if you would still like us to clean your windows.
Thank you for you past custom.
Best Wishes
Ian H