I remembering reading in the beta online manual something along these lines:
To earn guildmarks, you have to complete the entire quest using the appropriate class. So to get the Pugilist's guildmarks, you need to switch to the proper class before starting the quest, and keep to that class for the entire quest until you finish it.
You can't get guildmarks for the class you are playing because that's not the guild that's interested in you completing the quest...
Edited, Sep 29th 2010 8:09pm by NayliaMR