The final task of the Discover phase is the establishment of a diagnostic agreement. Diagnostic agreements are informal, verbal agreements between the sales professional and the customer that lay out the ground rules for a constructive engagement. The agreement prepares for the beginning of the Diagnose phase of the sale process. A diagnostic agreement sets a professional tone for the continued conversations between the salesperson and the customer and sets the stage for open, unfettered communication. This is accomplished by setting limits on future conversations, thus assuring customers that they will not be forced into situations in which they are not comfortable.
The effective diagnostic agreement explicitly defines parameters for continued conversations, a proposed agenda, the participants, and feedback plans. It sets up the flow and specifies individuals who should be involved and topics to be covered. It also specifies mutual "homework"—what facts and figures we need to check for symptoms of the customer's problem, what information and resources the customer will bring to the meeting, and what information and resources the salesperson will bring. This is unique in the sales world where getting in the door is usually considered the ultimate goal of the first contact, but it is a standard feature in other professions such as law, medicine, and consulting. When we assign homework, we cause customers to begin to think about their situations, the specific symptoms of their problems, and the impact they have. We involve them ahead of the engagement, and we signal our intent to discuss their situation in more detail.
After the salesperson and the customer create a diagnostic agreement, the Discover phase is complete. The salesperson knows that he or she is spending time in the best place, and customers know that they are dealing with a professional who can be trusted and will treat them ethically and with respect.
Discovery is a term used by lawyers to describe the process of gathering information on which they will build their arguments. Because we've borrowed that term from the legal profession, it is only fair to let a lawyer have the last word about this phase of the sale process. Gerry Spence, who regularly appears on news programs as a legal analyst and is the "winningest trial lawyer in America," devotes a full chapter in his book, How to Argue and Win Every Time, to the importance of case preparation. He pegs his success to the fact that he spends more time than his opponents to prepare to enter the courtroom. Spence, who has never lost a criminal case, declares: "Prepare. Prepare. Prepare. And win." 
See Gerry Spence's How to Argue and Win Every Time, p. 134 for excellent practical advice on effective communication.