Filip, A., and L. Voinea. “Understanding the Processes of Customer Acquisition, Customer Retention and Customer Relationship Development”. International Journal of Economic Practices and Theories, vol. 2, no. 2, Apr. 2012, pp. 62-67, http://ijept.eu/index.php/ijept/article/view/understanding_the_processes_of_customer_acquisition%2C_customer_.