In my (limited) experience sales people exist to convince people that products have value. This is mostly useful when the people purchasing the products are incapable of evaluating them (see: "enterprise sales"), or when the products don't have enough value to sell themselves. Look around you. How many of the things that you've bought have been sold to you by sales people?

The concept used to have more merit. Lots of things our parents bought were sold to them by salespeople. Most of those same things you and I have purchased without.

Today most of the time I see a salesperson, I see a smokescreen for a shitty product.