Which game is widely credited with pioneering the 'microtransaction' model for cosmetic items in Western markets, leading to the retail innovation that transformed gaming economics?

The gaming industry has dramatically transformed how virtual goods are sold and monetized over the years. In-game purchases and virtual economies have become multibillion-dollar retail innovations that changed how developers approach game design and monetization. Test your knowledge about this revolutionary retail strategy that has become a cornerstone of modern gaming business models!

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Team Fortress 2 (2007) with its introduction of purchasable hats and weapons
World of Warcraft (2004) with its premium mounts and pets store
Call of Duty 4: Modern Warfare (2007) with its weapon skin marketplace
Second Life (2003) with its virtual land and item economy