Yes, Taobao is a mega marketplace where you can buy everything from tissue paper to dresses cheaply.
As the market is so large so there could be devious sellers selling replicas or fake products. 
By following mentioned tips, you can protect yourself from such devious sellers or faulty products:
Always check the reviews and buy from sellers or shops with a high number of good reviews.
Read all the good and bad reviews and look at the uploaded pictures of the reviewed item by the reviewer.
Reach out to the seller for more details on product availability or pictures before buying.

What makes Taobao.com products so cheap?
Taobao.com is aimed at frugal Chinese people.
It is the regular shopping destination for more than 80% of Chinese online shoppers.
Opening a Taobao shop for free has attracted many people from all over China to become Taobao sellers.
Since one Taobao search will show you all the prices from high to low, they compete for sales even more than real shops. 
They must set their item price as low as possible to attract customers.

Taobao has a sales volume of 8 million while Aliexpress has a sales of 0.3 million. 
Taobao has 1 billion products, while on the other hand, Aliexpress products are available on Taobao at low prices
Because of this sales count, Taobao is estimated to be ten times as opposed to Aliexpress’s.