This is a really good way to make a lot of money.. my guild did it for an hour and I made over 400G in drops and stuff...
What you do is kill the first robot at the beginning... then move onto the second mob of trash.. Kill all of them accept for the one that looks like a bird (see screenshot.. hes marked with a triangle)
Once you kill ALL BUT HIM... the entire raid needs to run out of the instance.. the leader can then reset the instance, and that mob will respawn-- robot WILL NOT respawn.. but that second mob will-- this works every time.. you can just keep killing that same mob over and over... they drop tons of epic Gems and lots of mob epics :-)
Happy Farming
EDIT: OK mistype... you acctually want to farm the 3RD group not the second.. so just kill the second and move on and follow these directions for the 3rd mob... thanks
DO NOT KILL THE ONE MARKED WITH A TRIANGLE>> AS SHOWN BELOW :-)