You can report such a player to a GM, although you'd need strong evidence in the log to proof intentional griefing instead of blatent incompetence. (Such as having agreed upon lotting for seals in chat, then proceed to lot each seal and having the other BLM cast Warp II as soon as it became obvious he missed out on all 4 seals in treasure. (As opposed to someone warping you 5 seconds before drops because an afk person did not pass.)