I do get every spider out of every corner if I can see them, and I can't see any of them when I'm doing the tops, some of those spiders nests take more than a quick poke with the brush to remove.
I can't see the upstairs sills either, I do run the brush along them but not going to climb any ladders to check. If you are not getting complaints why worry.
I don't take any special care cleaning the brushes either, the downstairs brush looks like I combed a dog with it sometimes, soaking a brush in a bit of the pure stuff, sure aint going to get rid of all those cobwebs.
They are only made of pure silk anyway.
I do take more care if I know that I have to do the insides.
Another misconception IMO is the reliability factor, most customers don't give a dam as long as you don't go too often. I was working today on monthly accounts last serviced on the 3rd July, Two customers asked if I had been on holiday, the others said nowt.