I've been to quite a few Sephora's in my time and I feel like the busier the store, the more rude the employee's.
There's a Sephora in a all but falling down mall near me (seriously hobo's sleep in the mall) and they have the NICEST employee's. I think they're so eager to help because they're so bored!
Then there's an extremely busy- tourist, filled mall near me, and the employee's there are rude and almost impossible to ask anything. I think it's just environment. They probably deal with annoying little girls all day at that one or have a hard time watching for theft etc.
Just my theory!