The getting exp from killing issue is ridiculously easy to solve. Give the PC's as much (or even slightly more) exp from using skills and smart thinking to resolve encounters as they would get for defeating the encounter in combat. If they sneak or talk their way past the troll, give them the same exp as if they had killed the troll. Give them 10% more if you want to encourage this kind of behavior. This is already built into the game where traps are concerned. PC's already get full exp for traps wheter they bypass them or blunder through them and survive. It's really that simple.