Of the many things to be aware of in a negotiation, the three types of interests are arguably the most important. The sooner you can identify the three interests, the better positioned you will be for negotiating. The first type of interests are "shared interests." No tricky definitions here as these are interests each party has that are the same. An example of shared interests in populations of people would be: 1. better education 2. low unemployment 3. low crime etc. Everyone wants these things and of course because they are good. Workings towards these interests will produce win-win scenarios. The second "interest" in a negotiation is "differing interests." If "low unemployment" is a shared interests, a differing interest parties could have would be the resolutions to reach that low unemployment. Some may argue for tax breaks for the corporations because with less taxation they would hire more workers. Others would argue that tax breaks should be for consumers and their spending will demand more jobs. The last type of interests in a negotiation are differing interests. To reach an agreement, one party usually makes a great sacrifice. These are when the interests are the exact opposite.
This information typically comes out. They may not make it easy but it is hard to hide. We usually are busy trying to think of what to say next instead of listening and paying attention to non verbal language.