This isn't as hard as it sounds. Definitely best to do this one using stealth. Take out the camera guard and the other guards. You may want to go around and kill civs outside since they can end up causing problems. There will be civs in the side alley, out the back, in the car shop next door, and walking on the sidewalks. Once ready, take over the store without allowing any civs to exit the building, if even one civ gets past the door, it will fail. If a civ leaves the store even before you mask up it will fail so restart immediately if you see a civ walk out. If you have other players with you, then cable tie all the civs, if playing solo, cable tie as many as you can and make sure you're running skills that keep civs down for longer and yell at them in between moving loot. You can't kill any civs inside the building either or the achievement will not count.