I know its not easy but try not to take it personally. On the domestic side there are some people who are never going to be satisfied because no matter how good you do it, it will not be done the way that they would do and therefore (in their eyes) its not good enough.
We have a few like this over the years and we just say sorry that we aren't able to meet your requirements and move on. There are plenty of other potential customers out there.
We had one where there were some issues because of the staff member missed some things and the customer complained so I said fair enough no charge, money back we will do it again next week with more experienced staff and if thats acceptable you can pay us then. My missus who is the best cleaner in the world! went and minted the place, spent extra time etc and the cow never paid.
So as long as you know you have done your best, just get over it.
It gets a bit trickier when you grow and other people are doing the cleaning for you. You get a phone call but because you weren't there you don't know which version is true.
Life is too short
Mick