This tip comes from the Selling Power archives:
Never ask a question without first explaining why you’re asking.
Nirenberg says, “Just asking a question puts the listener on the spot. However, if you let him know why you’re asking, it makes him a partner,” Nirenberg goes on to explain, “People with sales backgrounds often avoid asking questions because they think that the talker controls the conversation. That’s not true because the listener can always tune you out. In fact, you’d be surprised how often you’re talking to yourself during a sales call.”
That is a good tip. Asking good qualifying questions is crucial for successful selling. However, most people have experienced a salesperson who takes this approach to an obnoxious extreme. I have seen them rattle off question after question like a machine gun. You could just see the prospect shutting down.
The key is to soften the questions before asking them.