Don't buy Half Life 2 used. RIP OFF REPORT

The makers (Valve) of the video game Half Life 2 created a thing calledSteam.
What is Steam?
Steam is a download verification system that you MUST install and register for (although free), in order to play Half Life 2 or any other game by Valve/Steam.There is no way possible to play a Valve game, or anyValve game without downloading Steam. The reason is that the games that you buy from Valve have about 95% of the game on the discs. After you install Steam, they will then ask you for your CD access key - also known as the game's serial number. This CD key is then uploaded/added to your Steam account for only you to use. Once this key is verified and registered to your Steam account, Steam will download the remaining 5% of the game onto your PC and then you will be able to start playing. This CD key is not transferable. Someone else can notuseit. Now thisalone is not a bad thing. For one, having your CD key registered to your own Steam account prevents others from pirating the game. However, when you are done playing the game and you want to either give it away or sell it, the new owner will not be able to play the game as the game's cd key is already registered to YOUR Steam account - therefore the new ownerwill not be able to register the game under their own Steam account. Therefore, you will NOT be able to play the game. There is NOTHING you can do about this. Steam/Valve will NOT reset your cd-key. They will NOT transfer the cdkey to your Steam account. DO NOT BUY A USED STEAM GAMEFROM okay OR FROM ANYONE ELSE.It will be useless. Please understand, there is no way to shareSteam accounts. There is no way around this. Once that cd key is registered to a Steam account, you can not un-register it. You can not re-use that key on another Steam account. You can not transfer it. It is essentially locked/bound to your Steam account. Valve customer service will tell you the same thing. Go a buy a new game from Best Buy, or any other reputable retail stores.
If you give it to a friend, and they install the game on their PC, they will be required to download "Steam". Once Steam asks your friend for the cd-key on the discs, it will reject it stating that "That cd-key has already been registered to another Steam account. Please re-enter a new cd-key". There are NO ways around this. Your friend is now stuck with a game that wont play.
Therefore, buyer beware. If someone on okay is selling a used Half Life 2 game - STAY AWAY!
NOTE: This also goes for Half Life 2 Episode 1, Episode 2 AND ANY OTHER VALVE GAME as they ALL require registration of the CD key.