1. Negotiating skill is a skill as any other soft skill.

2. If somebody consider that he doing the same job (have the same skill) it doesn't mean that it's true.

That’s how sales work unfortunately

You pay the asking price if the product provides you enough value. Negotiation is simply setting the asking price, which is absurdly mundane in a free market economy. In fact, not setting an asking price - thus letting the buyer decide what he pays - contradicts norms.

The metric of “how well you do your job” is highly subjective anyhow; between an employee, their manager, their product manager, their coworkers and HR there would be significant variance of opinion.