I have this problem from time to time, i tackle it 100% business like.
for eg....
Mr Edwards says leave it every other month or Mrs Jones says it looks as if its gonna rain ect ect,...My solution... If you want it every other it goes up by £1.50 to £2.00 and then if you miss even more months its im sorry but i cant keep you on the rounds as im only after reg cleans as im running a business.
and the old fav its going to rain..my solution.......ok if you dont want them cleaned because you think its going to rain then i cant clean at all as it rains all the time in the uk and there's no point in cleaning your windows, but thanks anyway...
as a rule of thumb i do mention all this when i puck up new customers i make it clear that the odd shower wont dirty windows and what with the back gates ect, i make my self clear and that norm does the trick...
i dont even go to 3 times if they dont want it i wont clean,its that simple, you will always pick more up, i wouldn worry pal.......