I think the reason he wants your account is to use it to scam people that are in this forum, he knows you are a reputable member in this forum and any information that comes from you will be believed by any forum member, he just wants to use your reputation to scam people.
Is good that you tagged him at least people will be very careful with him, I'm sure he may have messaged a lot of people too, this set of people should be banned from this forum in other to prevent this thing he did from Happening again.
Those that sell there account should know that they are putting people in danger especially if you are a reputable member in this forum, they will use your account to scam people which is not good so let's always kick against or reject such offer of selling our account.
If you are not interested in the forum anymore you can inform the moderators to ban your account or you can just leave it.
If you must know, account sales is not prohibited in this forum, transfers of ownership of accounts can be done at anytime. However, just as almost everyone has noted, account sales puts everyone of us at risk if the buyer is a scammer.
While account sales is allowed here, I think there should be strict rules which ensures that every transaction that involves transfers of ownership of accounts should be done publicly so everyone becomes aware that the account has changed hands. Anyone who fails to abide by that rule should be banned.
This way, members of the forum will deal cautiously with the account so they will not likely become victims of trust.