The difference between a personal and professional reference letter is that a personal letter focuses on demeanor and character, whereas a professional letter focuses on job-related skills and performance. Many employers focus only on professional reference letters as they are more fact-based and job-specific.
Both personal and professional reference letters examine the positive aspects of a potential candidate for a job. In a personal reference letter, the writer typically focuses on the ways in which the candidate shines as a person. For example, the writer may go into detail about the candidate's honesty and forthright attitude or the ways in which the candidate is friendly and courteous to customers. These types of references give a human aspect to a candidate's application, helping distinguish the person from the accomplishments.
Conversely, a professional reference letter exclusively focuses on the candidate's performance in a particular job. The writer may choose to highlight specific job skills that the candidate posses, such as knowledge of industry-specific computer systems or a willingness to work overtime to complete a task. These references provide more insight to the facts listed on a candidate's resume, allowing the potential employer to see the ways in which the candidate implements her skills.