SAP Working Student interview questions

Easy going, only a quick coffee corner session with a manager and some co workers. We mainly talked about prior expieriences, what I expect from the job etc. Recieved the offer about a week later.

The invitation to a face-to-face interview came 1 month after my online-application. I arrived 20 min earlier than the appointed time, but the receptionist forgot to call the interviewer while keeping me waiting. So I assumed that the interviewer had slight bad impression about me being late. Then I was told that we had to do the interview in the canteen, because the meeting room she booked was under repair for whatever reason. After the interview, the interviewer accompanied me to the exit and told me that I would get informed about the result 1 week later. However, two weeks after the interview I got a rejection letter stating that they had to consider other applicants. Anyway, I didn't ask for the reasons of the rejection. But then in the third week, I got another email from the interviewer saying that they are expecting me to join their team and asked me for my starting date. I don't know whether they were rejected by another candidate and turned to me pretending that nothing had happened. But this recruiting is really unprofessional !!!