There should be something like a Mercenary Guild for dungeons in addition to the systems we have right now. The guild would have its own ranks and currency used to buy Glamour Gear. There would also be a ranking board that players could view to see the top Mercenaries for each Job Class.

The way the system could work is a player goes to the Guild Board and either enlists as a mercenary or browses for mercenaries enlisted for each job class. Content with higher difficulty would have a bigger currency bonus for the mercenary along with other factors, like if the one who hired them never completed that content. Additionally the player looking to hire the mercenary could view how many times that person has cleared that piece of content as well as their "Reputation Points". After the dungeon the player who hired the mercenaries would have to choose weather or not to award a reputation point to every player that helped them as Guild feedback.

There would need to be some restrictions to prevent people from just running the content over and over with the same people. Perhaps the person looking for help can only hire the same mercenary once a day or can only use the guild service a few times per day.

What I like about a system like this over the duty finder is the incentive to help other players while also encouraging courteous behavior. It also creates a competition to be listed as one of the top mercenaries for your class while also offering rewards to those casually participating.