Continuity mistake: When Margaret is getting rid of the evidence of Billy Hahn visiting her, she crumples up the papers in his file and tosses them onto the file. The next shot showing her getting her gun out of the drawer, the paper is gone, then a different angle shows the large crumpled wad again, then again, a new angle shows an even bigger crumpled wad.
Continuity mistake: When Margaret smashes the glass in the frame, she bleeds onto the label of a file folder. In the next shot, the blood is on the folder and not on the label.
Plot hole: After Margaret kills Mike at the end, she leaves through the door that is right next to his corpse, leaving her fingerprints on it, since she is not wearing any gloves. Under these circumstances, the police surely would have done some forensic investigation and dusted the doorknob for prints, which would lead back to her. Considering Margaret moved up from being a psychiatrist to a lively con criminal, you'd think it would occur to her to clean up a little bit, but she gets a happy ending.
Suggested correction: As she tells Mike, she's out of control. I don't think she planned to kill him, but he goads her into it by telling her she really hadn't learned anything and he played her. THAT was the point she learned the lesson. She took the risk and killed him. The doorknob fingerprints were a risk, but not much of one since a lot of people probably used that door before the police got there.
As for many people using the door after the murder, probably only one person might have used it if they opened it from the hallway side, only touching the hall side knob. That person would have immediately seen the body and called the police. Anyone on the baggage handling side wouldn't have touched the doorknob. Still, Margaret is not in much peril from fingerprints, since we are led to believe she has always been a "good person" who would probably never have had her fingerprints taken.
Continuity mistake: At the end, when Margaret shoots Mike, for the last three fatal shots, the gun is pointed in a direction that would not hit his body and would instead shoot the wall, slightly to his right. This can be seen in the from-behind, overhead camera shot as she fires at him.
