After Oliver cuts Felicity loose, Felicity removes the scarf from around her neck. Yet in all the shots after it is still there.
After the Huntress is arrested and taken to the station, she is not wearing any of the black eye makeup under her mask. It's unlikely that she would have been allowed to wash it off so perfectly once they got to the station.
Slade Wilson claims that the anti-aircraft system feature featured in this episode is the Russian-made S300 system. In fact it looks more like the shorter range Pantsir S1system.
When Detective Lance is arresting Helena a shot shows him pointing his pistol toward the camera. You can clearly see the inside of the barrel is of a reduced diameter showing that it is not a real firearm.
When the alarms go off in the precinct during Helena's interrogation the two police officers exit the room into a corridor filled with smoke. This goes against the most basic police procedure of safeguarding your prisoner. They would have, in real life, uncuffed Helena from the table rail, secured her handcuffs again and the transported her out of the precinct together. She certainly would not have been left alone in the room with the door closed.