Mwuh, everyone's hair acts differently, people should try and go to someone who is A) good and B) they have been seeing for a long time! When you cut certain lengths off hair depending on the hair type it'll look shorter. Like, for example, my mother is a stylist and when she cuts two inches off my hair, it looks like three because I have wavy, but my sister it would look like five, because her hair is curly. It all depends on the 'weight' in your hair. When you go to the same hairdresser they will learn your hair and you won't get so many bad cuts. All hair acts differently, in reality the first time you're with a hairdresser, they are completely guessing how it'll react. For example, when my hair was down to my hips, it was poker straight, then I cut it to chest length and all of a sudden I had this really wavy.. mane thing. Neither me nor my mother(also my hairdresser) expected this because my hair had always been straight, thank god it turned out well otherwise I would have been upset
(ps I am not saying you should not get upset if you get a bad hair cut! That is okay! Just try and be understanding ; ; )