I've not had that comment often from custies. When I was new to the game, I used to say nothing, and got on with the job. I don't really rush when I'm working on domestics. That's half the battle won. The other half, I think, is pricing so you don't have to rush to make a profit and hit your daily targets, if you have them.
I get the odd clever custy asking how many houses we work in a day etc, and you can hear the cogs wirring in their heads etc. If they aren't happy or begrudge someone earning what they think is too much for such a low skill job, then let them cancel.
Millions of customers, only about 50,000 to 70,000 window cleaners. It's always easier to find custies than it is to find a windy.