Why get negtrust?
The campaign is open to the masses, it would be very bad if greed in participating in this bounty was included in order to increase stake through tuyul accounts/alt accounts/fake accounts.
The reason is because campaign managers are including it among the rules not to join with alt accounts, that if alts are known, the person will be removed from the campaign.
The worst thing is, You can be banned permanently.
You can not be banned because you joined campaign with alt, but the campaign manager can remove the person and its alt. Also both accounts and other all know alts can be tagged.
At Bitcointalk there are many loan services, even unsecured. Many are exposed to neg-trust by lenders
If a borrower do not default a loan and not paying, I have found it hard for a loaner to tag an account that borrowed. Some loaners will give the person just neutral tag is the most common. But if borrower do not pay and left the forum or do not dialogue with the loaner positively, why not the loaner shouldn't leave negative tag. I expatiate this based on the insecure you included.
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 noticed their is more focus on account selling than buying unless the buyer are shit posters, scammers and of anything that can not do this forum good, but they are left with neutral tag if the account change hands. But for anyone known to be selling account, the person should expect several negative tags. Both account buying and selling can lead to scam is the main reason for them being bagged.