To be frank with ourselves, it is not all clients that we must retain. Most of the times, there are some clients that are not meant to be working with more than just once. This set of clients are insatiable. You keep on working for them but they don't appreciate the work. You should not retain those ones. Apart from that, you don't retain clients that don't believe in you. It is a must for the freelancers to understand the clients first before deciding to retain them or not.