you can have confidence today. Learn your products well (their benefits) and use a concept called Anchoring to anchor your confident feelings from other aspects of your life where you are very confident. See Anchoring in my free persuasion articles
Like most skills persuasion and personal skills comes from having the right attitude and after you have had a lot of practice.
The attitude is one of service to the customer and desire to be THE BEST at what you do i.e. selling.
Always be reading and listening to other sales trainers and skilled salespeople and you'll learn something from just about every one of them.
Read a bunch of the free persuasion articles (above link) on this site and you'll get some ideas. THEN, use them, assess them, practice them and you'll find you are selling more easily and closing deals more often.
Hope this helps, Greg
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