Character is often revealed by how someone treats people who cannot help them.

How someone treats a person who cannot affect their interests is close to a direct measurement, because nothing else is influencing it. Waiters, junior colleagues, someone whose influence has passed, anyone in a position of no leverage. What appears there is not adjusted for advantage.

Use it as a read on others and, more usefully, on yourself. Notice your tone with people who can do nothing for you and compare it with your tone toward people who can. If there is a difference, it is worth closing, and it is closed by attention rather than by resolve.