I agree with the others about re-thinking the hiring of professionals. You would be mazed at the kinds of industrial-strength cleaning products they have access to that the regular consumer doesn't.
We had friends who had a child with severe respiratory difficulties. They had a caty, which they had to give away, and were advised to have the house thoroughly cleaned and sanitized after the car was gone, to get rid of the "dander" left behind. My friend is a reasonably good housekeeper, and even she was amazed at how much cleaner the house was.
There are people who can clean up a house after a gruesome murder, so professionals can do a lot.
And, I agree with you, when we were house-hunting, I was amazed at how filthy some people's houses were, and these were houses they were trying to sell!!!! I consider myself a "normal" housekeeper....my house is lived-in, clean enough, but I am not one of these neurotic nuts who have everything in its palce every second of the day either. One would think that if you were trying to sell your house, you'd clean it up, get rid of the clutter, and not have dirty clothes and laundry baskets strewn all over the floor. Yet I saw that more often than not.
Amazing...