Men & Magic says this:
As characters meet monsters in mortal combat and defeat them, and when they obtain various forms of treasure (money, gems, jewelry, magical items, etc.), they gain "experience".Now, the phrase "mortal combat", if taken literally, means that someone has to die, but if taken to mean only "someone might die," then the word "defeat" could be interpreted much broader.
You can defeat a monster by subduing or capturing it, as some later editions make clear.
You can also defeat a monster by making it run away in fear.
You can defeat a monster by tricking it into giving you what it wants.
Later RPGs that follow the D&D model, and even D&D GMs, seem rather loathe to use defeat in a broader interpretation. But if you want to award someone experience for successfully arguing with the king, why not use the same xp award you'd use for killing him? If an adventurer kills a couple goblins and the rest break morale and run, why not give full xp for the number of goblins that actually attacked?
Similarly, obtaining treasure could be broadened. If you help the king reclaim an outpost, why shouldn't you get xp for the gp value of the outpost? If you craft a magic item, some GMs will actually award xp for the value of the item. Why not award xp to Hercules for cleaning out the Augean stables, based on the improved property value of the stables?
It seems to me that a lot of "role-playing experience" can be explained in terms of defeating (in some sense) monsters and obtaining (in some sense) treasure. It always surprises me that people are reluctant to use these standard formulas more liberally.