I don't normally market a job or “sell” a candidate during an interview. I have found that by asking great interview questions, and having everyone on the interviewing team ask great interview questions, I don't need to sell. One of my clients is convinced that they need to sell during the interview.
If you too, think you need to sell the candidate on the job or the company, first you have to know what's attractive to the candidate. That means you need to know more about why the candidate is leaving/considering leaving his current job.
I sometimes start with a question like this, “Why are you leaving your current job?” You might hear a good answer, but more likely not. Too often, people are reluctant to say they want more responsibility or more money or a different product. More often, I'll start with a question about previous job changes, “Tell me why you went to the company you're working at now. What attracted you to that position?” Now I have some information about why the candidate went there. Now, I might be able to ask the why are you leaving question, but I'm more likely to ask about previous moves.
Once I know what's attracted a candidate before, I can say something about that in this interview–if it's true. (Never lie or even just stretch the truth in an interview.)
When I changed jobs back when I was working inside organizations, I changed jobs when I was no longer having fun learning new things, or if the company was about to go under. So, what attracted me was the ability to learn new things, and know my paycheck was relatively safe. As an interviewer, I can use that knowledge and talk about learning new things and the financial outlook for the organization.
So the way to market the job during the interview is to learn about the candidate–especially why that candidate is looking for a new job. Do that with behavior-description questions and maybe an audition, and now you'll have enough ammunition to sell the job in the interview. If you need to.