The Dar Traders 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)
They were surprised when Danika Meanwhile could perceive the Doctor, as he had died six times before. They had gained their ability to trade and resurrect the dead from a previous trade they made. (AUDIO: The Death Collectors)