Ann Baker has a long and colorful career in casting in Greater Boston. During the 80’s she put actors to work in Spenser: For Hire, the hit ABC TV detective show. Now this gifted and enthusiastic teacher trains actors in how to audition for commercials. In the first part of tonight’s class she fielded questions and debriefed students on what it takes to be a professional working actor in Boston. In a nutshell: training. She had students read commercial copy and gave candid, productive feedback.