Background: I work full-time as a software engineer and I go to graduate school doing a Ph.D. in computer science part-time. I work full-time so I can support myself and pay bills. Working as a Ph.D. student means that I can teach or research but it doesn't pay much. The pay is almost nothing. So that's why I work full-time and go to school part-time.
Interview: I have been interviewing at company X and they gave me a very generous offer. I am being very underpaid at the place I currently work at but I have a lot of freedom so I can use the time to work on school work. But I am 85% to 90% done with my Ph.D. and I feel like I can get much better jobs upon graduation. I am literally writing my thesis and papers so I present my findings.
I interviewed with 8 engineers and the 9th person I interviewed with would be my manager at company X. She kept saying, "we don't have challenging problems to solve that requires a Ph.D. student", "why a Ph.D. student would want to work at a company X" and etc. Very discouraging remarks. I felt like I was trying to convince them why they should hire a Ph.D. candidate instead of hiring a junior developer.
The HR person has been very friendly and they spent a lot of time on all the interviews and I feel bad rejecting the offer. I don't know whether I should be honest saying "the manager was very discouraging and I feel like she was under pressure hiring me". They tried every interview challenge but they failed to find something I couldn't do.
I am not sure how to reject an offer. I have never done that before. If I am honest with HR will I burn the bridges behind me? I don't think I would ever want to work at this company but I live in a small city, so who knows. How to reject an offer?
Tl;dr Their offer is very generous but it means I lose my time flexibility and I feel bad rejecting their offer. The manager's remarks didn't help. Maybe I shouldn't have wasted their time so I am feeling very bad.