There are various theories told about declining sales & valuation of Flipkart but one reason I could see is that they failed to enable the customers to choose the right products. In e commerce sites, the biggest challenge is to ensure quality & pricing of products where third party is producing/selling the products. Amazon overcome this challenge by forcing the customers to rate all the products they bought. It puts pressure on the seller to ensure quality & also it helps the customers to choose the right products based on customer feedback.
The last time I bought items in Flipkart is when I returned 3 of the 5 items I ordered and I am happy with all the products that I bought in Amazon based on customer rating. E commerce is here to stay, will become big and will create the organisation of the future, Flipkart need to just look for ways to serve the customers better, rest all just noise which they can ignore..