Almost all business processes require negotiation. Consider negotiating with a customer for a delivery date for ball bearings, negotiating price on a large order, negotiating your annual increase with your manager, negotiating an achievable quota for your sales team, or negotiating additional resources for your project.
On behalf of both your project and your customer's business objective, you will need to negotiate the scope commitment for your team. The team should also keep in mind that, in many cases, the customer may have already developed the skills of negotiation and will naturally use them in their discussions with you and your team. Therefore, if you are a team leader, project manager, or project champion, you should develop these skills as well. Negotiation is a professional business activity. It is not a particularly difficult process, and it can be done with integrity, grace, and style. Take the opportunity to gain some training in this process; your human resources department can probably help, or you may want to take an external seminar. Failing that, you should at least familiarize yourself with some of the rules of the game. For example, a good overview of the negotiating process can be found in Getting to Yes [Fisher et al. 1983], which can be read in a few hours. They recommend a few helpful guidelines for every negotiating session.
As you negotiate with your customer, your guiding principle in establishing the baseline should be underpromise and overdeliver . Doing so ensures that the inevitable vagaries of software development, unanticipated technological risks, changing requirements, delays in the availability of purchased components , a key team member's unanticipated leave, and so on can be accommodated within your project schedule. If you should happen to run the one project in a thousand free of these unfortunate circumstances, it's OK: at worst, you will embarrass yourself only by delivering early! Even that would provide at least some entertainment value within your company!