Im not a fan of ambiguity. From that perspective, allowing account sales on the one hand, and red tagging them on the other seems to me like an unnecessary contradiction. It would be conceptually much clearer if those two elements were aligned: Either allow sells and dont red tag them until some wrongdoing has been performed with the accounts at hand, or dont allow them and give red-tagging all the legitimacy when it becomes highly suspected (with prove that, ultimately, should/could lead to the accounts being banned).
Currently, it seems like a baited situation, which brings no benefit to anyone.
Forum rules don't define guidelines for trust ratings, not to mention that what we call "rules" is actually mprep's unofficial collection of what moderators will try to enforce. If account selling was disallowed by the rules then we would hear no end of bitching that account trades should be left for moderators to punish and not red-tagged for. We would also open the pandora's box of having to add other untrustworthy behavior to the rules lest scammers start to complain that e.g. newbies with self-modded locked autobuy threads is not against the rules, etc.
I'd say let's not overcomplicate the rulebook with something we can't possibly hope to enforce to everyone's satisfaction and keep making our choices with our trust lists. If we want to see account traders red-trusted - let's include users who do that and vice versa.
Ideally forum rules as enforced by moderators should not overlap with untrustworthy behavior as labeled by trust ratings. And neither of those should penalize opinions, but that's a whole other discussion.