For this trophy, you have to have the second set of challenges completed from the Thieves Guild.
Thieves Guild Second Set Challenges
Perform a Leap of Faith (40 times) - Easy to get. Find a spot where you can perform a Leap of Faith and climb back up and repeat until you have your 40. Try and use a building that is close to the ground so you won't have to climb very far.
Climb a total distance of 1 km - You will most likely have gotten this early in the game if you like to climb on the rooftops. If not, you will easily get this by getting your 40 Leaps of Faiths.
Steal money with a Counter Steal (250A) - Counter Steals are done by holding the R1 button down and pressing the triangle button whilst in combat. They are just like counter kills where you have to wait until your opponent is about to strike and then counter. 250A shouldn't take you long to get, maybe about 12 guards depending on how much you get.
Once you have all those completed, hire some Thieves and go around killing random guards. Once you kill the guards, wait in the area until the thieves have looted their bodies and repeat this process until they have looted 50.