Tuesday morning  ChannelAdvisor, which tracks monthly same-store sales growth for third-party sellers on the Amazon and eBay marketplaces, announced sales trends for the month of March. According to ChannelAdvisor, growth of Amazon’s third-party sales accelerated to 26.2% in March from 23.0% in February, and 14% in January (see exhibit 1). On a two-year stacked basis,…