What makes billy assume that the landlady is harmless?

Billy assumes the landlady is harmless due to her seemingly benign demeanor and the cozy atmosphere of her bed and breakfast. She presents herself as motherly and welcoming, which disarms him and makes him feel at ease. Additionally, her unassuming appearance and the quaintness of the establishment contribute to his perception that she poses no threat. This misjudgment ultimately leads to a sense of foreboding as the story unfolds.