Am going to go against the grain and say that's an authentic bag - it is vintage, probably mid 80s or very early 90s.
Would I buy it? No, because it is eBay and I don't feel comfortable making this kind of purchase from there.
Edited to add that re. pricing, given the age, style and condition, the pricing is about right. Bags of this vintage/style go for considerably less than many other Chanel bags.
My only criticism is tmatelassé is not a style of Chanel bag. This is a single flap bag. Metalasse is the term used for that kind of leather/quilting, and as that is Chanel's signature for leather goods, they have never needed to flag it as such.