Online flash sale site Rue La La, which counts eBay as an investor, is exploring a sale that could value the company at around $400 million, people familiar with the matter said on Monday. Boston-based Rue La La, which has attracted interest from online shopping site Gilt Groupe, has hired JPMorgan Chase & Co to advise a potential sale, the people said. Representatives for Rue La La and Gilt Groupe did not immediately respond to requests for comment. Founded in 2008, Rue La La was acquired for $350 million by e-commence and marketing services company GSI Commerce, which was bought three years later by eBay.