I've had some very picky people, and sometimes I feel like they are not worth the trouble, but it really depends on their attitude.
When I get a complaint, which luckily has been pretty rare, I try to think of it as a suggestion and add the "missed" task to my "detail schedule." I do uncommon details on a rotational basis, some of those things only get done every couple of months or so, but customers really do appreciate the difference, even if they are not the "picky" type. Every time I get a "suggestion" I become a littler bit better at my job and my references are that much more glowing. I've also learned that when a brand new customer nitpicks, if they are a regularly occurring customer, you can tell them that you have the task on your "detail schedule" and that you are already planning on getting to it on your next visit.
At the end of the day though, there are always going to be those people you just can't please. If some people see even the slightest streak on their floor, that can only be seen from a certain angle, they will complain, yet they won't want to pay you for the time it takes to clean it on your hands and knees for that "ultimate clean".
Just my two cents. Curious to see what others have to say.