I have a lot of experience handling difficult clients, believe it or not. I used to work at Home Depot as a customer service associate, so usually whenever things don't go as expected or clients are unhappy with a certain situation, what I like to do is I like to ask them what they think I can do to make it better, whether it's rescheduling something or a refund if it's possible or just trying to offer them something that would equate to what we couldn't offer them before. If they aren't happy with what I've provided them in terms of options or they just become more and more irate, what I usually like to do is I stay calm as I possibly can and I try to see if some upper management level can help with that because it's best to avoid conflict with clients and just try to see if there's someone else who's like higher up in the chain that can assist them with their needs and probably provide them with a better answer than I can, but I always find it best to not argue with the client, not upset the client, and just try to handle the situation in the most manageable way possible that leaves all parties involved happy.