Airing on Wednesday, April 15, 2015:  Stephen Dubner, the author of “Freakonomics,” rejoins the Marketplace team to discuss the value of diamonds and their hard resale value. High jeweler markups and a limited buyer’s market for diamonds have created what’s called a “thin market” for the good. Next, some tax preparers are charging high fees and making dubious loans to vulnerable clients. We look at some of the controversial practices these businesses are employing during tax season. Also, the European Union has brought antitrust charges against Google, with claims that the company has taken advantage of the European market by using its search engine to boost its shopping service. Are monopolies always necessarily a bad thing? We explore.