Federal Trade Commission investigators have been interviewing small businesses that sell products on Amazon.com Inc. AMZN, +2.49% , 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, +0.41% and EBay Inc. EBAY, +1.35% .