In this articleWMTAMZNReturns on Amazon are free and easy for shoppers, but they're risky and expensive for the small businesses that sell a majority of the goods on the world's biggest e-commerce site. Returns have driven some sellers to exit the popular Fulfillment by Amazon program, while others told CNBC they'd like to leave the platform altogether.At the heart of the problem is a big rise in returns fraud, which has led to customers mistakenly receiving used products when they ordered something new. In ...