My last job yesterday was at a house way outside the city. WAAAAY out in the country. Carpet was absolutely filthy! Farm family who fits the profile of every cleaner in the world. One look at them and your mental image instantly flips over to FILTHY!
As I pulled out the vacuum, I went ahead and put a new bag in the garbage can and brought it in with me, cuz I knew I'd be emptying the cannister quite a few times. I vacuumed the whole house and got, at best, a handful of fluff. I got to looking around and noticed that, while the carpet was filthy, there was no dust anywhere. No bugs and hair in the windowsills and not dirt on the baseboards. I looked around and found her Kerby vacuum neatly put away in the hall closet. She saw me and said, "oh yeah, I meant to tell you that I already vacuumed."
Goes to show you can't always go by the "looks" of things.