Wal-Mart Stores, Inc. (NYSE:WMT) will start to allow customers to trade in used video games in exchange for gift cards. The gift cards can be used in-store or online at Walmart or Sam’s Club stores. GameStop Corp. (NYSE:GME) is the sole dominant figure in the used video game businesses, but with Walmart’s size it can sell trouble for GameStop. Investors are uncertain that GameStop can continue to maintain its competitive advantage in the industry with the entrance of a big player like Walmart. Shares of GameStop are down over 4 percent on the news. Walmart’s barter used video games business will start on March 26th.