Up until The Die is Cast, Garak's prowess is either legend or propaganda. Certainly, we get confirmation that his views of morality are so flexible, he could do anything. That said, I think we understand he was also ruthless. I think this perspective is solidified in Broken Link and Empok Nor. Where it best shows is in In The Pale Moonlight: the actor playing Grathon Tolar fully sells the dread that comes from being associated with Garak, and it is paid off dramatically with his assassination. The interrogation is an exception, a discontinuity: Garak turns on a machine and waits, acting with desperation when Odo does not heed.