Make the achievement for Dungeon Master more of an achievement, rather then something you can buy for a couple of gold’s. You can still buy a full experienced run, but you you will have to do it all yourself and not just join in at last boss for title.
My suggestion is a boss by boss achievement that leads up to the completion of the dungeon / path once all bosses have been killed by you.
Also a better overview of which bosses and even more so which dungeon paths you have finished would help. Both for guild organisation as for ones own tracking of what you done – over the course of a couple of months and different characters.