If the new owner proves trustworthy too, nothing goes against removing the red tag IMHO.
Do other DTs who leave red trust for account sales agree to this? I've seen accounts with several years old red tags saying they're bought. How long should an account be active to deserve a review?
I have no clue, and to be honest it is more of a theoretical problem since most bought accounts are only used to shitpost.
My point is, if I know of an account that changed hands, that has positive or neutral trust, it seems the right thing to do to put a red on it.
Next step would be to get all positive/neg/neutral trust originating from the original owner removed.
If necessary remove inactive DT members that have left said trust.
And then after a while if the new user was to prove himself trustworthy, it should be taken into consideration to remove/change the feedback to a neutral one.
Statistically we might see cases in which the new owner could be more virtuous than the previous owner. Then again it is all hypothetical.