Wouldn't it be a good idea to regain unused merits ? Merit hunting both merit sell and account..
One of the reasons of introducing the merit system was to prevent the process of buying accounts and then ranking up by farming posts and then use that to join new campaigns essentially defrauding them. What you say will defy that objective because once a user of an account uses those merits to rank up his new account he will jolly well have grown it to a decent rank for joining a campaign.
Merit was a side-effect of the account farming that used to go around in an uncontrolled fashion here. Those who did that are the ones who cried aloud at that time because they realized they had dug their own graves.

Also account sales are going to be negged at any suspicion of the person attempting to buy/sell. Specially if the person is of a rank. It is the only way to keep the forum clean from scammers growing and using the social connections that a person has used till date to scam someone who might know that username as their "friend" but now in the guise of that "friend" to scam them.