You should post bitcointalk by your senior position account. Also you should added how much money you want to sell this account.
Because if he post with his *supposed* Sr. Member account, both accounts will be tagged. And a tagged account is worthless.Or maybe because he has no account and it's just trying to scam someone.
If you really own a senior account, why have you been posting with this newbie account over the past 3 months instead of your sr account?
Farming accounts? 
Or the above ^
However, even if he is really selling an account, his posting quality must be shit, so you can't really join a signature campaign. And if anyone finds out, you will be tagged aswell.