Largely yes, although I have heard about a few mishaps where fakes were inadvertently sold. It doesn't appear to be their intention, but they handle a lot of goods.
i had made bids on several items.. well the Hermes goodies but never won.. had been offered several second chance opportunities but do not have a purchase from them yet so can't say much about the authenticity of the item in close proximity..
They sometimes sell vintage watches (I'm a collector of ladies' Art Deco watches). I've never won one of their auctions, usually because their reserve is higher than the value of the watch.