In my tabletop games I generally give XP for "encounters" not combat. You get the same amount of XP for making the bandits run away, that you'd get from killing them.
This encourages clever thinking.
But as KainLexington points out, you have to avoid double dipping.
But I do think you get XP for some social encounters. I leveled up after I talked to Kagha for the first time.
There are some milestone / conversation xp, but I agree it would be a fine balance to avoid double dipping and allow it when it is legit. Here we are assuming each "encounter" only happens once, but it is very plausible that you talk your way through one scenario with a person, but have another encounter with the same person, in which you kill them. If you spoke your way through it twice you would get xp for both encounters, but you also should get xp for both if you spoke to them the first time and killed them for the second. It makes sense, but could be tricky to implement.
