I think you can suss out plenty by the way someone holds themselves in an interview, are they articulate, confident etc, but the one thing I'd specifically be asking is what they are passionate about (in life, in general). Whether it's reading up on serial killers, playing in their band, rocket science, or attending church... helps paint a wider picture...
hahahah we had this guy start who had an awesome folio, jobs with foils and intricate printing techniques used, he was able to explain it, but when he started he was terrible. Didn't know how to do the simplest things... what you see is not always what you get.
Maybe ask about their weekends, see that they have a good life/work balance, see that they are sane people, thats just as important as qualifications and skills. You don't want a loose cannon.
I also think it's important to work out prospective applicants knowledge of your company. When I used to interview kids in my store, I used to keep them waiting for around five minutes and watch how they interacted with products. The kids who showed absolutely no interest in the store & stood there tapping their foot, were the ones whose application had a tendency to be quite weak. I once had an applicant who had no idea what I sold and seemed genuinely surprised when I ended the interview after she shrugged in response to the question.
I want prospective applicants to give me some information about my business. It's not to much to ask that if you apply for a job, you should research the company first. I don't want to employ anyone who doesn't feel passionate about their work and although no one is going to love your business as much as you do, I would expect that an employer should at least like the company they work for.