See, you prove the case by case argument. Legit sellers, hackers, scammers it's all different. There's not any way to really give blanket forgiveness as I mentioned a few days ago. You have to look at the facts of each case and go from there.
You are right, I think mostly each case has its own circumstances and we should deal each one separately. Everything should be proved, different things should be discussed. I myself leave not so many tags because I think I should understand by my own why do I leave a tag and did I understand enough to do that. I never do so just because someone reputable did so. When I vote for and against flags I read each case and make my own conclusions. If I'm not sure I just don't vote at all. The same I expect from responsible DT members.
There can be some obvious cases like negative tagging cheaters opening threads for selling unnamed accounts (probably hacked) or merits. But other cases should be proved and probably discussed. If account is hacked and/or sold after that I tend to think that a negative tag is justified if there are no argues for opposite. If there are reasonable argues it can get a neutral tag, but every account which changed hands should be tagged one way or another.