Heres my opinion
There will be many people charging an average price, there will be a few who will charge more than them and there will be one or two who will charge prices that will seem to be double or even treble the going average.
The person charging three times more than the average price may be no better in any of his dealings, he may not be a better cleaner, may not leave a better end product, he may be no more articulate and he may have no more etiquette than the average, there may be no other window cleaners capable or willing to clean at this level in his area
He may have a full book and putting in high prices because he isn't worried about not getting the work
He may be confident in his ability to offer a superior service
He may have that likeability factor
He may have charm and persuasion on his side
No one can specifically say what allows one person to charge much more than others, it may be one thing, it may be many things - I personally applaud people that don't run with the herd and people that aren't restrained by the going rate.
Whatever will be said on this post I believe that when you have some or all of the above you shine with confidence and that confidence is infectious and people want your service and your confidence allows you to charge your worth.
£350.00 for one days work is broken down to about £35.00 per hour - whats wrong with wanting to earn that.
Some of us may not have ever seen that income hour after hour - day in day out but it is out there and people are achieving it.
Window cleaning is a cash rich business and I read posts last week about window cleaners cleaning conservatories where the householder already had a window cleaner but did not want to clean the conservatory.
Not everyone wants the work and not everyone can clean well so with a conservatory costing anything from £2000.00 up to £20.000 and more - it is an extremely valuable extension of the property and if cleaning them is marketed properly then this should be the normal price to charge.
I applaud you for valuing your time and your service so highly - well done that man - I believe you are an example that others ought to try and emulate.
People will say I can't get that sort of pricing round here - that is easy - set yourself apart from the average window cleaner and market your service better than theirs, offer a better quality service and there is no reason why you cannot be making that sort of money.
Rob