Is this like a shortcut for merit?
No. Its very likely a scam.
Personally, I would not allow this to be permitted and would punish any attempt of selling account with a ban/temp-ban.
The forum accounts get sold to scam people and other shady activities. Best to ignore these threads.
is this within the legal frame work of bitcointalk.org?
shouldn't it be illegal or something ?
Attempting to buy an account would get your account a negative trust. The administration does not take any step to prevent it so the DT members have to put that mark to warn others.