Which game is widely credited with popularizing the 'microtransaction' business model for cosmetic items in Western markets around 2010?

The gaming industry pioneered new retail models that have transformed how digital products are sold. In-game purchases and virtual economies have created billion-dollar revenue streams that didn't exist two decades ago. This poll tests your knowledge about a pivotal moment in gaming retail history that changed how developers monetize their games and how players interact with virtual goods.

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Team Fortress 2 with its hat economy
World of Warcraft with its mount store
League of Legends with its champion skins
FarmVille with its virtual crops and animals