Players are in full control of their character’s actions, including how the character feels and perceives their environment roleplay-wise. However other humans are an unknown variable. You don’t know what festers in the mind of your fellow man, whether you can trust them or not.
You should have no idea what goes on inside the mind of your fellow man, and making contact should involve a lot of risk but with the possibility of reward in the form of trade, training, and companionship. Unfortunately, NPCs are rather predictable and buggy right now.
I suggest that there be hidden NPC-specific traits or scores that determine how they’ll act in-game.
Trustworthiness: A NPC with a high trustworthiness value will never betray a character and will honor their deals, they also make great companions. While a low value would result in a NPC most likely attempting to rob you, attack you, or if they are a companion… betray you once their loyalty to a character is shaken.
Loyalty: A loyal NPC will never leave a comrade’s side, while a low loyalty score will result in them bailing at the first sign of trouble. A NPC’s trustworthiness would likely affect how their departure from your service will play out, such as stealing a bunch of your items while you sleep and running off or merely leaving peacefully.
Bravery: A very brave NPC will stand their ground against assailants despite serious wounds or being outnumbered, while a coward will run away from combat if they are so much as scratched.
Recklessness: A very reckless NPC will actively seek out danger and attack anything that comes close, even disregarding traps and other hazards such as broken windows and barbed wire. A very cautious NPC will only fight if absolutely necessary and generally avoid traps and hazards.
Competence: This would determine an NPC’s skills, stats, and equipment when they spawn. A very competent NPC is a formidable companion and a dangerous foe, while a very incompetent NPC is pitiful and likely won’t survive much longer on their own.
This is so far just a rough idea, in an attempt to have NPCs be more dynamic. Feel free to improve upon my ideas or debunk me.