Problem now with duty finder is there is absolutely no consequences for your actions.
Best thing would be to add a rate this player option on leaving a duty from 1 to 5 starts with the option to leave a comment.
(A players rating would start at 3 stars and moving it to even 2 stars or 4 stars would take a significant number of low or high ratings to weed out one off bad days etc. Also you could only rate people that you were not grouped with beforehand and a 3 man premade rating a 4th person would average out and only count as one rating.)
Then ideally when you get the 45 sec or so popup you could examine your potential group mates comments and average rating. Other then the score and comments nothing else would be displayed so you could not judge on class\gear\race etc. At that point you could thumbs up thumbs down a possible troublemaker or just cancel out all together. If the majority thumbs down they get kicked and a new person is brought in from the queue.