This NPC is a target for the rogue class mount quest Hiding In Plain Sight.
Auctioneer Xifa is an auctioneer in the Valley of Strength AH (far right one) so this mark is very well guarded by both guards and by players who you might have managed to avoid thus far. I managed to kill him before I was massacred by 9457048574 guards so it's definitely doable but expect to need to corpse run after.
Your mark is not very tough on their own, but there are of course guards, NPCs, and potentially players that can and will aggro. Your best plan of action for each of them is to burst down the marked target and then vanish and not bother with the other NPCs if possible. For this reason, I believe the quest is much easier to do as Sin or Sub.