I bought a hair style with cartel coins in the appearance designer. It looked nice enough there, but I immediately noticed issues with the physics once I started moving around.
It's especially bad when dismounting, after which the hair style clips through the character's head and stays there, making the back of her head look like in this screenshot:
https://i.imgur.com/BmF55nj.jpg
Edit: There's also a transparency issue when viewed from the front: https://i.imgur.com/XqMHKC0.jpg
There's also clipping when running around and especially while jumping. These problems aren't apparent during character creation, but instantly become noticeable once you start playing.
In the appearance designer, this hair style has number 53. This is a female human character.