We have to understand what is a necessity and what is classed as a luxury.
Petrol is a must so we pay the national price irrespective of where we live, we have no choice. To a degree its the same as alcohol as the nationals control the financial market.
Window cleaners are so different, they are mostly individuals who set their own financial targets and work accordingly towards them, this means that there will always be a varience between each other. The next thing to bear in mind is window cleaning is a luxury, so as a luxury they customer will look for the most cost effective supplier, a bit like buying your Flatscreen TV, we all shop around.