In some situations, you have to be harsh.
In this one, disaster can ensue if the tech does not show up to do the job. This isn't sitting a healthy kitten, a job you can test out a teen since cats can normally be pretty independent, and if forgotten for a day or two, will be okay. This is a senior cat with kidney disease, something that needs daily monitoring and likely timely and accurate food and fresh water provision. This cat can't be the "practice/try out" job. And if you can't show up to the interview, you were taking this like a "practice/try out" job.