Just a quick guide to warn people that when considering whether to buy a second hand online game (such as World of Warcraft, Halflife 2, Battlefield etc) be aware that you may not be able to play the game at all.
Although you may receive the box in the post including all the disks and manuals needed for installation, you may not receive the unique registration number that you use to create your game account online. Effectively meaning the nice box with the flash manual is useless!
My advice is to only buy these type of games if the description says "new and sealed". That way you can guarentee the registration number will be inside the box.