So, 

It would seem to me that you have a decision make. You can work on overcoming the introverted fear and embrace the sales path and all of the big personality that career path requires, or you can choose another career. 

If sales something you feel compelled to do then I would recommend joining a networking group that requires public speaking weekly. Toastmasters is great for that. And in Atlanta we have PowerCore. In fact, Wendy Kenny, the owner of PowerCore has a fantastic story about her own journey to overcome shyness and become a brilliant public speaker. I'd bet she could sell water to drowning man.