They washed 375 cars that day. And, the boss received increased productivity for the next month because he gave everyone a free car wash. That was one smart mom. She gave credit to her boss and raised money for her daughter's group and everybody won. Not every person is a cracker jack sales person.
Some people are introverts rather than extroverts.
What may seem to come naturally for some will seem like an insurmountable task to others. If you find that a few sales people are falling behind, put them in a team with an extrovert. If you can't do that, put them with an introvert. Two introverts together will find success because they will draw upon each other. They will lose fear of rejection and will not be afraid.