This is why I don't like putting my bags down when stores ask me. Are they going to be responsible for replacing my items if someone else walks off with it? I won't leave bags behind the counter even if they ask. Feel free to check it before I leave but I'm not putting it down.
(Not that you did that, it's just something to keep in mind)
Sorry those jerks took your stuff but it was nice of Sephora to help you out.