This is pretty twisted logic based on a plethora of attempted loopholes rather than common sense. Bob assumes OP and @TrustedAccountSeller to be the same person, even if they are not, if you really want to get picky about it, could you not claim that OP is an agent of @TrustedAccountSeller for facilitating the trade? I expect OP would have some financial reason for passing Bob onto @TrustedAccountSeller rather than just out of the goodness of his heart to make sure Bob got an account. That is, if they aren't the same person. Therefor, if a flag is valid, its fine for OP to leave it.
Onto whether the flag is valid or not. Its pretty clear to follow the chain of events and the money here. Then you apply whether or not it was intentional and whether Bob can be held responsible for it. Bob purposefully deceived OP for the sake of harming their business as is admitted. Bob didn't decide to back out of the deal because the conditions weren't favorable, they backed out because they never had any intention of buying anything, so arguing over whether the contract conditions were met or not doesn't matter.
Saying that the information isn't legally confidential and expectedly confidential are two different things. Unless you are suggesting that everyone should get NDAs drafted up before they do any business here, based on their prior communication with regards to escrow agents and warnings about negative trust, Bob had the knowledge that making the information known would do financial harm.
I don't care if you don't like account sellers or not, I'm not a huge fan of them myself, but you don't get to justify yourself as not a scammer because you scammed someone you don't like. SeW either as @TAS or their agent clearly lost monetary value as a direct result of Bob's intentional actions. All of the excuses I'm seeing are technicalities that are trying to weasel not out of the fact that Bob scammed SeW, but why they aren't allowed to leave a flag based on perceived loopholes in the warning flags.
Facts of the matter:
1. Bob intentionally acted in a manner that caused another user financial loss
2. Account selling is not illegal
3. You don't get to financially harm someone just because you are against what they do
We are opening a world of bad justification if we allow scams based on the reason the person scammed the other. This is akin to walking into a window store, taking a look at a few windows, telling an associate that you want to buy one, and before signing you just leave and smash the other windows on your way out. The issue isn't that you decided not to buy the windows...
Sometimes, a person has to break the rules to stand up for what they believe in. The OP is certainly welcome to open up a flag on this. However, I am not going to support it, just like I do not support the US Government prosecuting Snowden.