If they weren't interested, why did they agree to the appointment? This is generally a smoke screen. All prospects are doing is making you earn your commission by putting on a good dog-and-pony show.
This problem is actually on of the easiest to deal with because you know it's a bluff. Accept the challenge and put on a great show. Use the bluff as inspiration, and make the pitch of your life. Combine maniacal enthusiasm with persistent questioning and add one more element-blatant salesmanship.
Many prospects who use this ploy are in direct sales businesses or have a sales background. At the very least they admire a well-executed sale tactic when they see one. So give them what they want. Even if you don't make the sale, you'll establish yourself as a sales professional who isn't flustered by a little gamesmanship. That kind of reputation will get you in the door more easily the next time.
Excerpted from Creative Selling: Boost your B2B sales