Anyone can create a flag, but I don't think you'll find support for it.
Besides, bob didn't use his account for this, so the "warning" wouldn't help other account sellers. Just like account sellers who hide behind a Newbie account.
The accounts didn't make high quality posts OP, so bob didn't break your agreement.
Any chat screenshots to prove that this really happened? You know how hollow this accusation sounds without a proper screenshot. Also I find this matter better suited in "Reputation" since there is no scam accusation and is a matter about breaking an agreement.
See
https://bitcointalk.org/index.php?topic=5157334.0