One off cleans:
Unless they're next door to a job you're actually doing, they're a pain in the b*m.
Someone phones up: "Hello, I need someone to clean my windows, I live in a rented house and I've got to vacate by next (Mon.Tue etc) and I need the windows cleaning because I'll lose my deposit if the house isn't clean".
Now: They want quick service, you have to go and price it up, you have to make a special visit to do the job, you don't know until you start how bad it's going to be.
What are you, masochists?
It's going to cost you time before you even know if you're going to get the job, and there's no future value (repeat work).
Why should you subsidise these people? If they wanted their windows cleaned, why didn't they have it done during the (weeks/months/years) they lived there?
If you've already got a good lucrative business you don't need the hassle of "one offs".
So: Someone phones up: "I want a one off"
I answer: " My price starts at £50"
Occasionally I get one who says; "That's OK"
Otherwise it simply isn't worth my while.
Cheers,
Ian