Exactly right, this is why a market for assassination is unlikely to ever really emerge as a result of blockchain tech. People seem to forget that the only reason it works is because of the structured aligning of potentially competing objectives. There really isn't a way to decentralize an escrow service... I mean, you could try to leverage all the participant's competing interests - but that is a massive presumption and it doesn't even address the question of how. Not through PoW, because turtles all the way down, and not through PoS, because lol Ripple.