Not piracy, not used games in general, but the GameStop system to sell used games, because it affects games sales to honest, paying users particularly during the launch period, when many games earn the most of their lifetime revenue. Direct consumer-to-consumer used games sales, but also consumer-to-store and store-to-consumer ones, if they don't follow the GameStop model, are actually beneficial, they allow many hardcore gamers to buy more games without the GameStop system drawback.