I wouldn’t call the “red tag for switching hands” much of a reason considering any user can give positive or negative reputation. However, I would call the “This user's email address was changed recently” pop up suspicious combined with the other evidence.
Try to explain to me the reason for my actions in changing my password and email. I just foresee the scope of your imagination, and maybe one will make sense. But you would be very mistaken to think that the account changed ownership due to a password change. There can be many reasons.
But as for the negative tag left by a DT member, this is a pretty serious comment, and you probably don’t know the meaning of these ratings if you say that anyone can leave such a tag. The difference between any person and a person from DT is big.