Tate uses this example to display the efficacy of denying the sale to a Customer.

Customer: "I need two flux capacitors please"
Seller: "No Problem, let me check and make sure we have some. There's been high demand lately, so I'm not sure if we have any. What do you need them for?"
Customer: "I need it for <xyz>"
Seller: "Okay, we don't have any right now. Give me your <contact information> and I'll be in touch."

• By asking the Customer why they need the product, and allowing them to elaborate. We're helping them reinforce the fact that they legitimately need our product. This makes the Customer want the product more.
• Call him back after a while
  Seller: "How many did you need?"
  Customer: "2"
  Seller: "Okay, I can get a hold of two for you, but it'll be difficult. Are you willing to purchase now?"