Dar Trader were a race of traders.
They scavenged the dead and gave knowledge in exchange. They could sense whether someone had died or was going to die. (AUDIO: The Darkening Eye, The Death Collectors)
They were immune to Decay and could detect its levels. (AUDIO: The Death Collectors)
They saw the usefulness of Nyssa being a Trakenite. (AUDIO: The Darkening Eye)