I always prefer before and expect before if your new.
If its a guy I've seen MULTIPLE times not just 1 or 2 times.
I Don't mind after because I somewhat know your not going to try to scam me.( it has happened before when I was new..guy "Attempted" to short me 20 bucks..smh)
....if you prefer paying someone after that means your not sure about her level of service...I'm assuming...I get it.