i honestly cant remember the last time a customer said that to me...it was years ago now....
when i first switched i lost around 3 or 4 customers who didnt even give me a chance to use WFP......they point blank refused to have them cleaned with the pole.... 
most window cleaners have WFP near me now....even the stubborn ones......albeit using glassfibre poles,barrels and trolley systems or backpacks 
...theyll learn.....eventually.....
But maybe someone’s backpack gives a much better ROI than your all singing dancing , diesel guzzling, ego enhancing system does 
its not ego enhancing....if you want the quickest most efficient way of working with as little hassle as possible and a system to last you years and years then you have to pay for it......ive worked with backpacks and barrels,trolleys too....its a crap way to work,ive worked from old vans,ive used gas shower heaters and bottles to heat my water and everything in between......so i know what im talking about......
I disagree... my daughter works with me. we can either do a house each, or one does the back and one does the front, we both have a back pack. I have a transfer pump from the tank to fill them ... it takes seconds....then we are away ... no trailing hose..
then when finished just walk back...job done , no reeling in
I don't have to worry about freezing pumps etc, and on very cold days which are very few , I just fill my tank with hot pure water.
I have only worked, 17 hours this week, and have taken more than that figure you said.