Through negotiation or mediation, the goal is to resolve the dispute between the parties so each can at least have some of their needs met and both sides can move on personally, professionally and financially. That may be accomplished best by focusing on the issues, not the people or personalities involved.
The Interest-Based Relational (IBR) approach to resolving issues is discussed in a recent Lifehack article. It was created by Roger Fisher and William Ury in their 1981 best-selling book Getting to Yes. The approach suggests,