Blacklist is the term used to designate Amazon Kindle devices that were blocked from being registered or connected to an Amazon account because they were refunded, replaced, reported as lost or stolen. Blocking occurs through the Serial Number. If a device has been blacklisted, as of not being able to connect to Amazon servers, many features that requires it won't be availalle. It is impossible to reverse this, except on some occasions where the lost/stolen device returns to the original owner.
Changing the serial number with jailbreak doesn't seem to work, if the serial number has been changed there are two possible results: the number it was changed to is in Amazon's database already, the Amazon system will blacklist that number (killing both devices), or the number it was changed to is not in Amazon's database, the Amazon system will blacklist it.
Blacklisted devices have some limitations, such as not being able to connect to an Amazon account, change the device name, access advanced settings, access Whispernet, create collections, view Wikipedia summaries and make translations, etc. Basically the device will only be able to access the internet trough the Experimental Browser (Wi-Fi) and read sideloaded books, transferred from a PC by USB cable, in the "documents" directory, manually or using programs such as Calibre. A blacklisted device can be fake registered with jailbreak to have some of the features back, but it won't connect to Amazon servers and in case of Wi-Fi being enabled, the fake registration can be wiped out.
To update the firmware of a Blacklisted device, you have to transfer the update by USB cable, in the "Root" directory, and update the firmware in the device settings, as it can't connect to Amazon servers to download the update.
Remember that the use of a Blacklisted Kindle can be considered a crime, and you are responsible for it.
 Sales of Blacklisted devices
Be careful when buying a used Kindle, there are many cases in which the devices were sold blacklisted, but don't worry, this guide will help you:
 How to identify a Blacklisted Kindle
- Take a note of the Serial Number and call Amazon asking them if it's Blacklisted. You can see it in the device settings or in the back of the box;
- If the device is connected to any Amazon account, then it's not blacklisted;
- You can also try logging in to your account, if it goes successfully, then the device is not blacklisted;
- If it's Blacklisted, don't buy it, but if it's not, de-register it logging out from the previous owner's account, resetting the Kindle, and then registering with your account;
- Blacklisted Kindles are mostly sold by some people's suspicious ads in those stores below.
 Stores/Websites known for selling Blacklisted Kindles
- Craigslist (US);
- Letgo (US);
- MercadoLivre/MercadoLibre (BR);
- eBay (Worldwide).