REUTERS/Lucas Jackson/File Photo Amazon is a growing advertising and selling channel, and a group of companies promise brands e-commerce expertise and tools that they can't get directly from the e-commerce giant. Business Insider highlighted 18 of the third-party tech firms and agencies that are powering sellers' and advertisers' Amazon's business. Visit Business Insider's homepage for more stories. Amazon's advertising business continues to balloon and along with it, the number of companies that help brands navigate the ins and outs of advertising and selling on the platform. Business Insider identified 18 companies that are part of a cottage industry of Amazon-focused tech firms.