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.
