If they don't buy you, your product or service has no shot. They buy your message only if they buy you. Well it started from people giving lousy performances. You can do it if you believe you can. Don't confuse fear with lack of preparation.
Fear is a reactive state of mind and can be easily replaced.
Ask engaging questions. Questions about satisfaction, finance, technology, use of product, satisfaction with service, quality, or future. A question about them that makes them think and respond in terms of you. Make them laugh, but don't tell a dumb joke. You'll know one second after you tell it.