SPIN selling is a sales methodology that involves gathering information through four stages: Situation, Problem, Implication, and Need Payoff. The Situation stage involves learning about the customer's current processes. The Problem stage identifies pains and issues. Implication helps understand why those issues need resolved. Need Payoff helps customers see how resolving issues achieves their goals. The goal is to advance the sale through actions, obtain an order, or learn why no sale occurred. SPIN selling aims to make the sales process more effective through understanding customer needs.