They are definitely authentic and much like similar sites, such as Hautelook, Zulily, even Groupon and Living Social. Rue tends to be a bit more high end and there is another site that also offers very similar high end products but since I unsubscribed to that one, I can't even recall their name.
I have bought from them all at one time or another and never received anything that was not brand new with all manufacturing tags attached. They really are a great way to pick up clothing and beauty especially, at really discounted prices. I even got some lovely European shoes (flats) that retail for over $100 and I paid less than $30. The shoes are really gorgeous leather and the attention to detail was impressive.