When a candidate applies for a Sales position eg. Automotive; why is that the employer requires previous experience in same field?

presenting the product well,demostrate new features and safety

Sales process represent the company in front of customers and giving the positive or negative impression to the customer even if there is sales supervision

so no way to recorrect the customer impression

because of that ,experience is a must  

Previous experience in the same field are advantage because u can have knowlegde with the same field and can work without farther supervision.