Confidence is probably the most important fundamental for success in selling. Not only do you need to be confident about who you are and what you do, but you need to have confidence in the products and services you represent. Note that those are two different things.
First, confidence in yourself and your capabilities or strengths. This is even prior to having anything to sell.
Secondly, when you do have a product or service to represent – you additionally need to understand and believe in that as well.
Take a look at this short video on being confident for sellers, and gain some more momentum each day.