Happy customers are easier to manage than unhappy customers. 

You still need to spend a lot of time on them, but the work is much easier because the relationship is positive.  

How can we can we convert the unhappy customers to satisfied and satisfied customers to happy?  It’s not easy to give a simple answer... 

Certainly B2B customer relationships can improve with persistence, empathy and time. A few years back I inherited a customer which was in a bad state. It was a significant account which took us about 6 months of hard work to see signs of life in the relationship.  

In conclusion don’t get discouraged if things don’t turn around for a few months. They are testing you to see if you are genuine in your efforts to turn things around!