But can't the buyer show proof? Posts of selling the account by actual owner.
Not sure about this.
Apart from the negative feedback issue ranochigo raised, there is one more problem that I just found in the following Badbear's post.
I've gotten several complaints lately, from people who bought accounts that turned out to be banned or hacked, and also dirty accounts that were on the verge of being permabanned due to previous infractions. You're on your own in cases like that, we will not help you. Be careful.