Be sure that they are treated as Gold. Communicate with them . Find special ways to build a relationship with them. Thank them for their business. Use your best customer service people with them .
Some banks segment their customers by profitability.
When the phone rings from a profitable customer, their ACD uses ANI automatically to shift these calls to a specially selected Gold customer service team. Build equity in the process . Provide rewards for volume business and for length of service. Make it expensive to leave. Don't stress price .