1) Low pricing when compared to other online shops and at actual shop.
UPDATE Currently even Amazon and ebay offer low pricing. This is comparable. I mean, some product are high priced here and some are low.
2) Fast Shipping on select Sellers and quick delivery as promised with them. Basically the sellers Labeled Flipkart Advantage have fast shipping.
UPDATE This was till last year, but now only a few sellers like WS Retail have fast shipping.
3) Because they offer COD for all products they sell.
4) Good packaging with most products and no chance of missing any Accessory inside the package like invoice, handsfree, etc. If Invoice is not there, they will mail you on request. UPDATE Now they have introduced the instant billing system as of 2015. Also now they send Invoice only through email for most of their selling.
5) U only get Brand new Products on flipkart. NO USED PRODUCTS at all.