One way to prove or disprove it is simply time.

Jennifer Lopez appears with really long hair, a bob, or shoulder length within weeks or a few months. That´s why it just can´t be real. The same goes for Rihanna. For me she has no hairstyle at all; I can never take her hair seriously, and I don´t bother a second anymore.

There is this model on Hair4U who has repeatedly and believably shown that it takes her about four years to grow a bob out to tailbone length - she has videos with a timeline by which you can estimate roughly that it would take other women about two years, too, of constant growth to go from shoulder length to waist length, for example.

You just cannot sport real waist length hair on a whim after having had a bob one year before. There are limits to what the human body can naturally do.