Sujeet Kumar, head of Flipkart’s largest seller and its captive logistics business WS Retail Pvt. Ltd, has quit the organization, according to three people close to the development. Kumar along with another former Flipkart executive, Tapas Rudrapatna, controls 46% of WS Retail. Until 2013, WS Retail accounted for nearly all of Flipkart’s sales. Flipkart moved to a part-marketplace model in that year and is now accelerating the shift by adding tens of thousands of sellers this year.