For me, difficult customer needs to hear them out. Let them speak. Listen to their concern. Take note of the triggering words. Once they're finished talking, I always let them feel that I atleast catch some of their concerns if they mentioned multiple or the main main issue. So that, customers would know that I really listened to them. Next is to use my resources, to make sure that my resolution is based on their needs. Sometimes, explaining a specific situation about their account is a solution. After that, deliver the long term resolution for the customer's issue positively. If this customer doesn't listen, then I have to make good balance judgement between the customer and the company.