Customers come in all shapes and sizes, some tall, some short, some fat some thin, so what, I hear you say, has this got to do with window cleaning?
The point I am making is these are just the things about them you can see. Just as variable is what goes on between their ears but you can't see that.
Some customers are happy and easy to please, others are miserable and find fault with everything. (Some are downright weird!)
Thats why I never bother about them, cut them loose and let them go. You really can't please everyone. The mistake is trying to hang on to them. Gradually over time you build up a round of nice easy customers.