The best negotiators can find creative win-win situations. They're able to figure out what winning means to their counter-parties and are straight forward about what they're looking for.
I've never understood why some people are cut-throat negotiators. In the long-term, the potential harm to relationships doesn't seem worth the risk, especially because you're likely to negotiate with the same people again in the future. If people have bad experiences working with you, they're unlikely to give you the benefit of the doubt and will be less willing to compromise in the future. In other words, the way you negotiate, not only effects the current deal, but future deals too.
While you may not be able to quantify the goodwill you accrue from a negotiation, it's a key outcome to keep in mind. Remember it's a small world and people talk.