Here is a video with some wise words about selling vehicles. The only point I want to make about this video is one needs to understand there is a skill to making major sales. Selling a vehicle is a major sale.
Selling the polish to make the car look good is a simple sale. The skills required are totally different.
Unfortunately most sales people do not understand this. Nearly all books written about selling do not separate these skills. Notwithstanding this, good pointers are in this video for newbie sales people wishing to enter the car selling business.