Linus is shown looking at a fishing village (Menemsha) on
Martha's Vineyard through a camera lens. He pans across until he comes to a lighthouse. There is no lighthouse in Menemsha. The lighthouse shown is in Edgartown, clear on the other side of the island (20 miles away).
In one scene, Linus and Maude are talking while Maude is riding a stationary bike. When she stops, she keeps her hands on the handles with one handle farther forward than the other. As the camera angles switch back and forth, so does the hand which is forward.
When David is confronting Linus in his office, David enters, Ron and Ron leave, David slams the door. When he does this Linus leans back in his chair. The camera pans back to David for a line and then returns to Linus who is still leaning forward at his desk, not having had time to get back to that position
As Sabrina rides the train home from New York, she is photographed through the small vertically-rectangular windows of an old fashioned commuter train with sharp corners. Across the aisle behind her, the windows on the opposite wall of the train are broad and horizontally rectangular with rounded corners like a modern commuter train.
When David runs into Sabrina after picking up the Picasso, you can see the door to the traffic light controller box is wide open indicating that someone is controlling the traffic for filming. (If the box was open legitimately, the operator would not leave it unattended.)