So my question is, how does negative trust work? Do people neg people out of malice?
Yes.
Anyone can create any feedback they want. Feedback is simply a way for a user to say what they think about another user. If someone wants to say they don't like you, or that they don't think you are trustworthy, then they are allowed to say that. People who read that feedback can decide for themselves if they think the feedback is coming from someone that gives reliable feedback, or if the feedback is coming from someone that gives unreliable feedback.
Are there no ways people negged out of malice could appeal and revoke such wickedness?
No.
You aren't allowed to decide what someone else thinks about you. If someone thinks that you are untrustworthy because your name starts with a "C", then they are allowed to say that they think you are untrustworthy. It is up to each user to decide for themselves whether that feedback from that person is reliable.
How does the forum ensure folks don't get begged by meanhearted people?
The forum allows each user to set up their own trust list. This is a list of the people whose feedback the user trusts.
The forum also allows each user to choose whether they want to trust the feedback of all the people that are trusted by those on their own trust list.
The forum allows each user to choose how many levels of "trusted by trusted" the user wants to include.