Ok, looking at the shape of the voting, I'm discounting the votes for 1 in 10, as the results look the right shape (statistically speaking) without them.
So, the average vote was 4.07 (and if you don't discount the "one in ten" votes, it's 3.62)
So it might be said that the average guess on here was four people in ten have their windows cleaned by a paid for window cleaner.
Alternatively, the most common guess would suggest about six in ten.
Me? I'm going to go for "about half".
Thank you all for voting. The truth will set you free.
Vin