A few horrible things happened here.
First of all, the salary I negotiated was not the salary they ended up paying me. They underpaid me for almost six months before they finally agreed to give me what I had originally been offered in my interview.
Second of all, I was a café employee. We would frequently run out of ingredients towards the end of the night. One night, a woman came in asking for a food item that we could not make due to the ingredients being out of stock for the night. We asked her if she would be interested in another item, made that item, and checked her out. The next day, I was called into my manager's office and told I would be reprimanded because the woman claimed that she was not served at all. There are cameras in the cafe that can be checked, yet upper management chose to immediately give me punishment instead of checking all the facts of the situation. A few days later, upper management pulled me aside to apologize because I had actually served the woman. But I had already received the punishment and I was tired of being mistreated at that point. I hadn't missed a single shift (other than a time in January when I had a fever of 104 F), I did good work in the café, and I have good work ethic in general that I am not willing to waste on a place that lacks respect for its people. I resigned the same day I was apologized to.
Note that this was all done by upper management. My managers in the cafe are all sweethearts and I will miss them.
One final note, working at this job feels like being in highschool again with all the gossip. I'm very tired of how much management talks about other people behind their backs. The way they treat employees is incredibly unprofessional.