Insist on Using Objective Criteria
Don’t take offers at face value. Try to figure out the objective reasoning behind the offer. Just asking about the reasoning makes the other person evaluate their position. Once they are in an evaluation mode, it opens up the floor for you to present your reasoning.
With all the reasoning is on the table, insist on a fair process. Be ready to compromise between two equally worthy criteria. And be ready to walk away if the other party isn’t willing to compromise. Keeping a reputation as a principled negotiator will server you well in the long run.
Book: Getting to Yes