I need help with job interview. I work as a contractor in IT field.

I went through the routine of answering technical & behaviroral quesitons.

what should I say to the interviewer at the end that will convince him that I am interested in the job.

I just not good at selling my self. I am currently suffering depression now thus my voice might not sound enthusiastic to the interviewer. I tried to speak more enthusiastically but no avail.

one of the question interview ask for 1 of your strongest strength.
Should I just say that I am well trained to deal with customer service since I have extensive hands on dealing with irate users.

for weakness question: Should I say that I don't have weakness that might hinder my performance on the job? Is this a good answer?

I feel nervous on interview thus sometimes my eyes avert around the interviewer although my mind is focus on the question.

Do guys tend to avert their eyes in direct conversation with ppl than women?