Ask Why?
People have all sorts of reasons for not buying or giving an objection, and you shouldn't take "no" personally. The more you can put your ego aside and gracefully accept the refusal, the more you learn from the experience. So, assume for the time being that you've been turned down and your business with this person is done. Make it clear that you've accepted the reply. If you're no longer trying to sell him, you and the buyer will be in a more neutral territory, and you'll have easier time getting information that will help you. Begin by saying that you appreciate the time he's given you and ask if he would be willing to take just a few more minutes to talk about why he isn't interested. Explain that the information will be helpful to you in your job and you'd be thankful for the feedback.
You might not get a straight answer initially, because people are often uncomfortable with having said no and want to get out of the situation as soon as possible. They're likely to offer a pat answer about price or prior loyalty, but if you probe a bit you might find your way to a more substantial reply