As the other reply states, you have to ask open-ended questions. Sometimes, a Yes or No answer is fine, but not when you're qualifying the customer and this is the stage that makes a happy client- you can't possibly do this without knowing what they want, unless it's by coincidence.

If they become annoyed, and I wouldn't advise testing their patience, find a tactful way to get them to see that you don't read minds and that's what a lot of potential customers seem to think we do.