What if an NPC had a "Reward Pool" and that reward pool were given out upon EITHER successfully interacting with NPC, or killing them? That would totally eliminate anyone min-maxing the "system" by non-combat means and gaining the XP, and then returning and killing them.
That means that killing a popular quest quiver in a pub rise a ton of xp. Such a quest giver could be a simple fisher man level one.
Only deep consequence system could allow that. Otherwise killing such xp honey pot is too tempting. One sword swing and ... several levels ding.
Easily handled by simply setting a flag -- "quest completed"
if "quest completed" for an NPC, then ZERO xp for killing them.
...but, yeah, point taken -- quest-hub type NPCs might need "special rules."
