Trosky
Good to see that we see along the same line.

I don't think the £950 vs £600 TV argument is relevant to w/cleaning.
What if the price difference was £50 or even £100 - but one store offered a longer warranty, or included installation or a stand to put it on?
I got a custy recently at £20 when her current cleaner was doing it for £15. She was a recommend by one of my custies across the road. She phoned me, I quoted and asked why she was looking. She said her current cleaner (also wfp) was pleasant but was unreliable, and always missed a certain window. (pole not long enough, I guess) She noticed that her cleaner missed the tops of the frames above the windows (not due to vents either.) and only took about 15 minutes.
I said I might only take a couple of minutes more but that all those issues would be addressed. She took me on.
The point is that for a small difference of £5 in price (but a high percentage - 25%) people will pay more, trust you and keep you if you are reliable.