4. Buy-sell account
There are no restrictions on buying and selling accounts, which are stated in the general forum rules. But when the ownership of the account changes, it's not impossible that top members suspect account buyers will do things they don't want (such as fraud). This is why those who buy accounts often get neg-trust.
I don't think you can get a negative trust for buying an account. It rules says buying Bitcointalk account is "discouraged".
18. Having multiple accounts and account sales are allowed, but account sales are discouraged.
A neutral tag is likely to be given to a bought account with reference feedback to the change in password or posting style. IMO a negative feedback or red tag may be given in cases where the new owner is suspected to have malicious intent. Others had shared their opinion about this issue on this thread
Bitcointalk Rules..Bend/Break