The shorter the better
You have to ask questions that truly engage the customer. However, this doesn't mean you need to develop complex questions.
Source: Sales consultant/trainer Mark Hunter
Instead, the best tactic is to ask shorter ones. Long questions tend to result in short answers, while short questions will generally result in long answers.
An example of a great short question is, "Why?" In my opinion, there isn't a better follow-up question you can ask after the customer has shared with you some information.
Consider how your customers would respond to other short examples like, "Can you elaborate on that?" and "Could you explain more?" These shorter questions elicit detailed responses and that's just what you want.
On the other hand, asking complex questions often tends to perplex customers. Because they are not sure what you are looking for, they respond with the universal answer representing total confusion, "What did you say?"
Questions should not be your means of showing your customers that you are an expert. Save that for your statements.