I understand your concern, but people do the quest for the Soul equipment, why would they not pick the reward after completing it? Right now it is not possible to see if the chest was opened, only if the character still had the Soul War item on its item list, but is still not certain because they could have bought the item from another player. But every character that has the Base Revenant and killed Goshnar's Megalomania opened the chest because this was their quest goal. It would be nice if CipSoft put a special tab on Bazar which displays "Opened Chests" from difficult quests like these. But right now the only way to know if they did the quest or not is by the Outfit, since to mark it as "Completed", you need to go back and talk to the NPC, which a lot of players avoid because it's a difficult path.