Or, "Which aspects of our business are you passionate about?" You want to hire someone who's both qualified and has the desire to do the work. Otherwise, why would they work for you instead of the company next door?

Part of their answer will lie in their body language and enthusiasm. The other part will lie in how concrete their answer is. Get at the details by asking a follow-up question, like: "Let's say you're at home, kicking around, and doing something related to marketing. What is it that you're doing?" Perhaps they're reading their five favorite marketing sites, or analyzing traffic patterns of websites for fun, or writing in their personal blog, or optimizing their LinkedIn profile. Whatever it is, you want to be sure they're deeply passionate about the subject matter you'd hire them for.