Federal Trade Commission investigators have been interviewing small businesses that sell products on Amazon.com Inc. AMZN, -0.59%, Bloomberg News reported, citing several attorneys and at least one economist. The report said the FTC have been conducting interviews that typically last about 90 minutes and cover a range of topics, including what percentage of revenue their businesses derive from Amazon versus other online marketplaces like Walmart Inc. WMT, -0.24% and EBay Inc. EBAY, -2.73%.