Lets take a generic scenario, and leave Flipkart aside, at least for a while.
Suppose you are doing an online business, and people are free to write feedback on those pages against the products or service you offer to your customers.
Will you not be scared of negative reviews, competitive prices(some where else), negative review going viral, etc. And hence, will you not safeguard yourself against such possibilities? I would certainly take every possible step to safeguard myself(if I were in that online business).
So, as a measure to safeguard myself from possible negative events, I will hire professional content writers who can write some reviews for my products and services once in a while.
I would create a system which will filter negative reviews.(I will get at least 9 out of 10 reviews filtered by an algorithm.)
I will try my level best to moderate reviews put by actual users(the once who are not planted by me). And will not let their negative reviews published at any cost.
etc.
Wonder, if I can do something like for my business, why can’t Flipkart do the same for it business? Yeah, its unethical, but then certain things need to wait until the war is won!
[As a matter of fact, because of these very reasons people started their own reviews sites. Like the Mouth Shut . com, etc. However, even they are not to be believed 100% even they know how to make money via back-channel arrangements;) ]