Dear Mrs Custy
Sadly, due to winning a major contract in (name a town twenty miles away) I have had to consolidate my window cleaning round. Rather than me struggle to keep up with all the work that is flooding in I have carefully sought out somebody who will give you the service and regularity that you are used to.
Therefore I am introducing you to Shinum Heapfast Window Cleaners who have been in(name custy's area) for several years and who are looking to expand their family business and who in my opinion will provide you with a first class service.
Please be assured of my best attention at all times,
WW
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Or try this

'Ere missus,
I'm fed up wiv doin' yer windies as it messes with me dole kerlection and drug dealin activities. So I've foundjoo a rite propper geezer wot will look after you.
He goes by the name of Shaggnasty Carpet Kleeners (window divishun) and he will provide you with a service that is the mutts nutts!
If 'ee messes you abaht then let me know and I'll visit him with Mr. Baseball Bat.
Warmest regards,
WW