I used to think neutral meant Machiavellian.

But someone pointed out that neutral is more careful, morally speaking.

Neutral means you try to benefit yourself, without harming others or benefiting others.

The original model is:

Good - You benefit others

Neutral - You neither benefit nor harm others

Evil - You harm others

But the distinction between Boy-scout and Hero deserves emphasis.

As does the distinction between Machiavellian and Kamikaze.

Extended model

Angelic/Martyr/Hero - benefit others when it harms you

Good/Boy-scout - benefit others if it benefits you

Neutral/

Selfish

- don't benefit or harm others

Evil/Machiavellian - harm others when it benefits you

Demonic/Kamikaze - harm others when it harms you

The range of Boy-scout to Hero is how far you are willing to go to benefit others.

How good is your character?

The range of Machiavellian to Kamikaze is how far you are willing to go to harm others.

How evil is your character?

The range of Machiavellian to Boy-scout is how far you are willing to go to benefit yourself.

How selfish is your character?

Important to note here is that this is all about intention.

Intending to harm someone, but accidentally helping them is in the evil range.

Intending to help someone, but accidentally harming them is in the good range.

Intending to benefit yourself, but accidentally harming yourself is in the selfish range.

As this is all internal, it's quite difficult to tell the difference in others.

You can ask.

You can check body language for regret or shame.

But all this still has quite a margin of error.

We are probably more interested in how someone teats 'me and mine' over how someone treats others in general.

Also important to note is that in real-world people, instead of flattened fictional characters, all of this is situational.

It's context dependent.

To put out a couple of extremes:

How far are you willing to go to help your children vs parents vs friends vs random strangers vs...

How far are you willing to go to harm your family's murderer vs thief vs bully vs random stranger vs loved ones vs...

When you observe the results of someone's intention towards someone else.

Someone's behavior in one situation.

Because you want to predict that persons intentions towards you, in another situation or in general.

There is quite a bit of loss there.

Perhaps there are more useful things to do than judging people's character.

(src: based on D&D character definition)