Amazon (AMZN) -1.9% and eBay (EBAY) -2%, following markets lower, after ChannelAdvisor reports same-store-sales growth declines for clients relying on the companies in May. Amazon's growth rate fell to 25.8% (its lowest over the last 12 months) from 30.6% in April, and eBay's fell to 16% from 20.5% (auctions -18%, fixed-price +16%, Motors +30%). The numbers also aren't great for Google (GOOG), which is seeing rising e-commerce ad competition and has been tweaking its strategy: sales from search ads -0.8%, and comparison shopping (e.g. Google Shopping) +0.3%. comScore puts total U.S. e-commerce growth in the 14%-15% range.