Even though GameStop's CEO is confident that Amazon.com's plan to enter the used video game market won't be successful, it appears GameStop investors aren't as optimistic. Shares of the company dove 13% on Thursday, ending the trading day $3.54 lower.

Variety reports that Amazon.com's used game ambitions (and to a much lesser extent, Toys 'R' Us' plans) worried investors today, causing a huge GameStop stock sell-off. Used game sales account for 44% of GameStop's gross profit and having Amazon as a competitor in one of its most lucrative operations just doesn't bode well for its stock price. As far as we're concerned, competition among businesses is always good.

Shares of Amazon stock seem to be unaffected by today's news.

This article was originally published on Joystiq.

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