It costs money to hire Sales people, and if a company were able to sell its products entirely as a self-service option, that would help them improve margins. So people in the Sales profession have to justify their existence every single day - what have you done for me lately etc.
The only way to succeed in the profession is to show results, to help customers understand and extract the value of what they're buying so they can come back to buy more and tell their friends.
You might see Sales people succeed in the short-term by lying or cheating their customers but that doesn't last. Your reputation catches up to you. Depending on the industry, every one knows everyone else, and the only way to truly succeed in the long term is to make sure you create a win-win for both the customer and your employer, every time, on every sale.