ProPublica has a report today in which it warns Amazon shoppers about the results that they see on the shopping portal. It notes that people often hope that the results that come up first after a search are the best deals, and that's what Amazon will have you believe, but its algorithm doesn't work that way. In what may surprise many, in more than 80 percent of cases, Amazon ranks its own products, or those of its affiliate partners higher. From the report: Amazon does give customers a chance to comparison shop, with a listing that ranks all vendors of the same item by "price + shipping." It appears to be the epitome of Amazon's customer-centric approach. But there, too, the company gives itself an oft-decisive advantage. Its rankings omit shipping costs only for its own products and those sold by companies that pay Amazon for its services. Erik Fairleigh, a spokesman for Amazon, said the algorithm that selects which product goes into the "buy box" accounts for a range of factors beyond price. "Customers trust Amazon to have great prices, but that's not all -- vast selection, world-class customer service and fast, free delivery are critically important," he said in an e-mailed statement. "These components, and more, determine our product listings."