Actually is real or fake is up to you, since I can find many of these in taobao.
Firstly, you need to learn Chinese to understand how does taobao works.
Therefore, you have to go through it to understand why it is selling so cheap.
Does it selling cheap because of 11.11 promotion?
Another reason is probably DeathAdder chroma is an old model (the latest version is DeathAdder Elite).
Some seller claim that the price is wholesale price, they are selling just the mouse, without box, without manuals & stickers.
It is hardly to say 100% is fake product, since anything can happen in China.
China nowadays is different compare to 10 years ago because their country was became more advanced. They are able to make everything with highly quality controlled.