I've only seen 2 cases of someone buying an account, 1st one was a rogue in my guild who quit and sold his account. It went to a preist on our server who uses it for farming purposes, and later actually joined our giuld
(on the preist).
The second time was a warrior from the top alliance guild on our server. The guild didn't know anything about it until they took him to a BWL run and found he didn't have a clue what to do. Was later kicked when they realised it wasn't the same person behind the character, still unguilded
AFAIK.