You can’t please some customers.
Whether you have internal or external customers, you should always try to please them. If they’re happy with an interaction, they might come back. They might tell others. Business may grow.
I do think, however, that there are some people you might not be able to make happy. No matter what you do, how much you do or how well you think you did it, they’re not going to be satisfied.
So, what do you do? You continue to do your best. You continue to put forth your best effort. If you do everything in your power to provide the best, you’ve done your job.
Be proud of your contribution. Don’t get lost in what you didn’t accomplish. If you can say you did your best, you’ve done your job.