I qoute that house at £10.5 - west of scotland.
My advice is, you cant do anything if a customer tells you not to come back, but if you get the chance to justify yourself. Let them know that...
1. Some window cleaners, especially ones qouting unprofitable prices, tend not to be working legitimitly, are uninsured, not licenced so may have a criminal record, and as a fly by night wont be regular and most of all wont last, as they eventually get caught or get another job somewhere.
2. I hold a large number of houses in this area and if they only get one or two, you might find they dont come back at all.
3. You really do get what you pay for and quality is very important to a professional, however if someone is charging very low as well as sacraficing the legal requirements the quality of work tends to be pour.
...and if its a qoute you are giving the most effective reply is...
4. and the fact that this window cleaner who was charging to £6 isn't here now is evident to that.
I had one yesterday that I qouted about £20 and the customer said there last window cleaner was £5. Generally when you are of as much as that you dont get the job, but I managed to convince her that my price was fair.
Good luck mate.