Also, you probably shouldn't be afraid Amazon will check for the jailbreak certificate. It would cost more money to properly check every return than to just toss them in the to-be-recycled bin.
At least, no one has ever reported getting a warranty return denied, despite a number of people returning jailbroken Kindles to Amazon.
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Do not leave an active Screensavers hack on, though. That is a very superficially noticeable jailbreak indicator.
