In my opinion accounts should have no value at all. The previous owner was the person that contributed to the value that the account added to the forum. I have seen too many bought accounts that had a excellent post history, prior to the sale.
After it is bought, everything change and the posts quality dropped significantly. The tagging is a good idea, but it should be more visible. <Prominently displayed, like a Signature or Avatar as a separate entry or parameter in the user posts >
Let's be honest, a lot of the bought accounts are being bought to give credibility and reputation, to people who want to cheat the system or other people.
If we want to reduce scamming and crime in our Bitcoin community, we should be more serious about "cleaning" up on our own doorstep, <Our beloved forum> by stopping user account sales.