I had some guests gave me a 4 star in cleanliness because they found two hairs on the bathtub. But the whole apartment is super clean. I personally would not take one star off because of two hairs as I think one star means 20% off which is too heavy for two hairs found . But the guest thinks it differently. He thinks as long as it's not perfect he would give a 4 star in cleanliness. But you can always find imperfections in any businesses. This rating is very unfair.
I hope that Airbnb should pop up a guideline message when guests are about to give ratings. For example, 5 star cleanliness means 81%-100% of the place is clean. 4 star means 60%-80% clean, etc.
For overall ratings, they can give a guideline likes 5 star for perfect shower facility, polite and friendly host, noise level is good, etc. And 4 star means blah blah blah
That would give more fair ratings to every host and it would not cause the picky guests got cancelled.