If I may talk about the referrenced thread first, as I happen to be attending that thread, I think my stance for that case remains the same: I dive myself there just in the interest to reveal the truth behind it, the whole story. So far, unfortunately, the OP seems to get caught in a tangled web of his lies stories. Suppose I can get to the bottom of the case and --again, suppose-- he was lying about the gift thing, his post history still were/are not detrimental to the forum[1], he did not scammed anyone yet --or ever-- so I don't think I'll leave a negative tag or even a neutral one.
I just don't see the point of it.
Negative tag will be unjustified as the person did no harm, didn't fool anyone, didn't abuse any rule. While neutral tag will practically serve no purpose at all as the account is a pure bounty hunter. That thin-black numbers on his trust column will just serve to inform BMs that the account move hands, and most likely the campaign managers --if they're a wise manager enough-- couldn't bother less as long as if that person made a good posts and promote the campaign they're working on. So yeah, no purpose.
One thing that needs to be voiced though, is a possibility that the account is connected to several accounts, which leads to ban evasion. I've asked the individual in question about this matter and he's yet to reply me, but suppose that the final verdict is that he's indeed connected to those accounts and thus evading forum's ban, then the negative tag should be placed, but that's the only reason of the negative tag; ban evasion, not buying or receiving accounts.
Now, to address the issue globally, I personally think leaving a negative or neutral tag should be done on a case-by-case basis. No case has similar points and narratives and shouldn't be treated equally.
It leads us back to what happen after the account is bought.
Does the new owner use the account wisely? Post nicely? If yes, then why should they discouraged by negative tag and got all of their effort ruined? It's way past bedtime in my timezone so I am too lazy to dig the forum, but I recalled several cases raised about account changing hand on this forum. One of it that crossed my mind was a daughter of someone who passed away or something? I didn't follow the thread from the beginning, just got a summary of it, but IIRC she posted nicely, used the account wisely, got tagged and was forced to leave the forum for that reason. And what the forum got from it? We didn't get damaged by her existence and her posts here, but we might lose some potential by "banishing" her. Who knows if one day she developed into an excellent scam buster? Or build patches that helps the forum? Or spread awareness of this crypto to her friends and colleagues? So, as long as the new owner --whoever that is, my previous sentences were not limited to that specific female human-- use the account wisely, I don't think a negative tag is necessary.
Sure, they should have take the better way by building their account from the very basic level and climb up, that if their posts are good they'll reach high rank in no time so there's no reason to buy accounts, etc. but, it's already done, isn't it? The account is already bought, "damage" is already done, and the person --on this scenario-- put a good efforts and results on that bought account. I think the good outweight the bad thing. Maybe we can simplify it by turning it into a business POV. They invest in something, make a good effort on that investment and did no harm, so why should they be disturbed?
But umm... remember when I said earlier about case-by-case basis? Yeah, this is where my opinion get a little bit complicated.
If the bought account is a gleaming account though, high ranked member --I think it's suffice to say Sr. and above or maybe even FM-- who reached the position through earned merit instead of legacy, or account with positive feedback, then I think that bought account needs a neutral tag for the sole purpose of informing the members that at one point the account moved hand and the previous reputation --merit and feedback-- was not earned by the current owner. The tag serves as a divider of quality and reputation between the old and the new one created by the new owner.
Moving to the other side of the table, if the account was bought for the case of spamming, low quality post --which, sadly, as mentioned above by Ratimov, is the most likely to happen cases here-- though, then it deserves a tag. But even then, that tag was placed due to the post quality itself, one that's been placed to plenty of accounts that never moves hand for the very same reason.
Now, for the case that the account is sold, this is a completely different scenario than above.
The account seller, IMO, deserve at least a neutral tag to mark him for future reference. For the why he deserved a tag while the previous case should be treated after reviewing their posting habit is simply because I am sure that seller did not, does not, and will not care about how will the account be used after it moves hand. He couldn't care less if the new owner is a spammer, or a scammer, or both. Thus, clearly detrimental, and thus, a tag.
Of course this thread is strictly limited to account moving hand by being sold and bought? Not stolen and hacked? Because that two deserves a special room in hell, they go straight to jail.
[1]At least that's what perceived by several honorable members of the forum who attended that thread too, and I choose to just trust them as I haven't give his most recent posts a read to be able to put any weight on any side of the scale.