Continuity mistake: In the hardware store, a bright blue sign in the background reads "Electrical" in reverse. When Jake hands Monk his card a few shots later, the camera angle hasn't changed, but the sign has turned around and now reads "Electrical" forwards.
Continuity mistake: When the victim's niece is crying and Monk is quizzing her about the house, the position of her hands changes instantly several times as the camera reverses angles. She holds her hands to her face as she cries, for instance, but in the very next shot, her hands are down at her sides. Next cut, they're up to her face again.