What selling point would you use if you were to sell your product service to your potential customers?

What selling point would you use if you were to sell your product service to your potential customers?
One of the key aspects of the role you have applied for is to be able to sell products and services to our customers using a conversational style of selling. Please provide an example of when you have had to persuade a customer to buy a product or service which they may not have previously wanted or known about and what was the result?