Am I required to issue a full refund to a customer if I have performed work that they claim they are unhappy with?

I had a customer bring me a Dodge Ram that needed a great deal of body work done as well as painting. I repaired the body damage to the best of my ability and painted the truck. When it left my garage it was beautiful. They contacted me a few days later and said they had issues with it. They brought it back and we went over the problem areas. The issues they pointed out were not there when it left my garage. I explained to them that I had put a bunch of other customers off in order to squeeze the truck in and that I needed to catch up before I could get them back in again. They messaged me on facebook last evening and asked for a refund. I am wondering if I need to issue a full refund or just for materials? Am I to receive nothing for my time and labor? They have said that they are going to press criminal charges against me if I don''t have them a full refund by this evening. I don''t see how they can press criminal charges but I am just looking for a legitimate answer before I reply.