Final answer:
The major approach for increasing customer margin that is NOT mentioned in the text or discussed in class is churning activities.
Step-by-step explanation:
The major approach for increasing customer margin that is NOT mentioned in the text or discussed in class is b) Churning activities. Churning refers to the process of acquiring new customers to replace those who have left. However, in the context of increasing customer margin, focusing on reducing operating costs, being more selective about the customers targeted for acquisition, and increasing customer satisfaction and loyalty are the key strategies.