After Marnie and Dylan get out of the cab and walk up to the first building, they're not carrying the luggage, then in the next scene, they have the luggage again.
When Mrs. Piper is paying for her groceries in the supermarket, she swipes her card with the magnetic strip up. Therefore, the card wouldn't register. She then goes on the punch in her pin and accept payment.
When Gwen Piper is talking to Aggie in the soup pot at the beginning of the movie, it sounds like Aggie addresses Gwen as Linda. However, she is really saying 'Gwenda' as a nickname for Gwendolyn.
When Marnie and Splendora are in the royal room, Marnie's eyes change from blue to green in multiple shots.