The eyes are the window to the soul, or in some cases, the window to believing an npc is a dead fish wearing pants.
Look Alive plugin adds a single component, the LookAliveComponent. Adding one of these to your characters give you instant, life-filled eyes. They eyes use their own animation independent from the rest of the actor. They automatically make eye contact with each other based on distance and viewing angle. They sometimes wander around, or sometimes stare blankly for a moment. These eyes will make your character look alive. All you need to do is add this component to your character, adjust the position, IPD, and radius of the eyes. You can set the location for the eyes to focus on from your blueprint, and you can turn autofocus on for eye contact to occur automatically.
For characters from the marketplace, you can simply export the mesh, delete the stock eyes, and reimport. I did this with the Dark Military Characters.