Getting the customer involved
Next time a customer stalls out on you, ask them as a next step to review something for you. It might be a report you're going to email to them or it might be something on a website.
Source: Sales consultant Mark Hunter
The key is to see if they will provide some input to you. This simple activity is one of the best ways to measure how serious a prospect is in doing business with you. Someone who is serious will do what you ask them to; someone who is not won't.
Their response to what you ask them to do will not only give you a sense of their level of commitment, but also may give them a quick "out" to indeed tell you they are not interested. Either way, it allows you to move forward. Either they are a serious prospect or it's time to drop them and move on.
Another great tool to measure the seriousness of a prospect is to ask them to share with you some proprietary information. It might be a question you ask regarding the strategic focus of their business or how their volumes are for this month.
It can be almost anything, but when you ask them a question that requires them to reveal something that is not known outside the company, you will quickly determine if the customer has confidence in you. Since confidence is what customers are really buying, then a key to knowing if a sale is going to occur is if they will share with you something of proprietary nature.