How and why? I don't get the point about salesmen here.

Companies are not perfect optimizers. Arguably not even that strong. If someone in Purchasing is willing to reward their buddy instead of picking the best vendor for the job, well, that happens. It's noise. Doesn't change the overall behavior of the company. And it only happens within limits - do it too much, and the person in Purchasing will find themselves fired, maybe even charged with a crime. If they're too good, maybe they can kill their own company - much like a sickness can kill a human. Other companies will then be more vigilant.

Also worth noting that companies strive to improve their process and develop various means of ensuring and enforcing accountability - this, in essence, is trying to reduce the "noise" of individual humans within the larger AI of the company.

People who professionally influence companies, i.e. those whose job it is to understand corporate decision-making, focus almost exclusively on the dynamics of personal relationships. Salesmen, B2B marketers and even activists all use human behavior as the foundation of their techniques. This thing about corporations being monolithic being-like entities is a "theory without a practice;" we can look to the people who empirically deal with corporations to see that they do not find it useful to think that way.