(customs) The amount by which imported merchandise is sold in a country below the home market or third country price or the constructed value (that is, at less than its “fair value”). For example, if the U.S. “purchase price” of an imported article is $200 and the fair value is $220, the dumping margin is $20. This margin is expressed as a percentage of the import country price. In this example, the margin is 10 percent. See dumping; fair value.