I just found the listing, and this listing should have screamed fake to you.
Her other bag (Fendi Spy) is fake, she has 0 feedback, and her Starting Bid is $500.
I PROMISE you that an authentic Hermes Birkin will not sell below $4000 (The cheapest I have ever seen).
In fact, brand new Birkins sell for OVER retail on Ebay and used Birkins will sell for retail on Ebay. They get away with this because there is such high demand and the waiting lists are closed. Even if you manage to get on a list, it will be 3 years before you can get one.
If you PM me your price range then I can let you know what I find. A 35cm Birkin retails close to $8000. Also, please specify color, leather, hardware, and size.