Bargaining for Advantage -- the book by G. Richard Shell

Shell repeatedly cites Influence, as well he should, given that he spends the bulk of the book applying Cialdini's insights to the bargaining process. Unfortunately, Shell does not have the same talent for rationalizing subject matter, so one has to sift through the book (well worth the read) and build its ideas into a mental model, as the one provided has omissions and does not lend itself to visualization.

Refactoring Shell, the bargaining process has three elements:

Alternatives
Having many alternatives puts you in a superior bargaining position, so it makes sense to take time to enumerate all the possible other solutions and then rank them by cost or benefit. A good opponent will have tried to figure out your next best option, i.e. what will it probably cost you to walk away from the deal?
Information
A Bargain can only happen when two people have an overlapping range of acceptable prices. The more you know about the other person and yourself, the more options you will have to craft a mutually beneficial solution that maximizes your benefit / cost.
Influence - aka The Dark Arts
Everyone has psychological needs and reflex responses, and we can use them to increase the odds of a better outcome. The more you know about what makes you tick, the better defense you'll present. Likewise, gauging the other person will make your offense better.

Shell rehashes a bunch of Cialdini in his explication of The Dark Arts, however Shell leaves the Information side of mapping out your opponents needs curiously unexplored. On page 85, he describes a $1.6E10 negotiation for the sale of Core States Financial to First Union: Core's CEO had cold feet, not because he thought Core wasn't getting enough $$$, but rather because he felt he was betraying the communities (knowing that First was probably going to consolidate/liquidate some branches). So, First created a $1E8 charitable foundation to help those communities, and the deal got done.

Identifying and Classifying the various psychological needs would help immensely, as satisfying those needs will often cost less than increasing your primary offer. I think many people operate under the illusion that we negotiate based on one metric (say price/value), while our decision process actually takes into account many other variables.