Final answer:
Dr. Trumbell must seek supervision or personal therapy to overcome his countertransference issues, following the APA's Ethics Code and possibly referring clients to other practitioners if necessary to maintain professional standards.
Step-by-step explanation:
Dr. Trumbell should recognize his own countertransference issues when he discovers that his personal feelings towards his neighbor are impacting his professional behavior with clients who resemble his neighbor. The APA's Ethics Code requires psychologists to manage personal biases and maintain professional boundaries. Dr. Trumbell should seek supervision or personal therapy to address these feelings and prevent them from interfering with his therapeutic work. If his feelings are significantly impairing his competence, he may even need to refer his clients to another practitioner while he works on these issues. This acknowledgment and action are vital in demonstrating respect for diversity and maintaining ethical and professional standards in community psychology research and practice.