Four kinds of question, in order — and the third one is where the sale is actually made.
The SPIN sales strategy comes from Neil Rackham's 1988 book Spin Selling, based on twelve years of sales research.
A sequence of questions that moves a buyer from describing their situation to asking you for the solution. Unusually for sales advice, it came out of observing thousands of real sales calls.
Situation. Understanding the situation as it stands now. Necessary, and inexperienced sellers spend far too long here — buyers find it tedious to be asked what they could have looked up.
Problem. Recognising the underlying problems currently being experienced. This is where the conversation becomes interesting to them.
Implication. What impacts or implications result if the problems are not resolved. This is the step that separates it from ordinary questioning, and Rackham's research found it is what distinguishes high performers.
Need. What needs or next steps are required to solve the problems and avoid the impact. Ideally the buyer articulates this, not you.
The implication questions do the work. A problem the buyer has lived with for two years is not urgent until somebody helps them add up what it has cost.
It is one of the few sales methods built on evidence rather than assertion — twelve years of observed calls rather than one salesperson's experience. It applies to considered, higher-value purchases, which is most professional services.