I received a nice email from a colleague that a previous post, on interviewing for a usability job, had helped her interview a prospect. That post was written for job seekers, so the email prompted me to post from the other side of the table. Here's what to think about when you're conducting an interview.
Have they tried out the product, or researched the organization? If your website or interface is publically available, prospects ought to have tried it out. If it's not, they at least should have found out all they can about your company. This question is my version of the white socks test: it's a easy way to quickly separate out the real contenders.
Look for broad skills. User experience is a developing and expanding field, touching on design, writing, marketing, QA, and customer support. Your job description might not call for knowledge of one of these topics, but since a tech company's needs change all the time, it's a plus when candidates show evidence of their adaptability.
Experience in multiple domains also has value. Here, look for a T-shaped resume -- broad skills across the top, with deep knowledge of at least one specific domain. Research shows that teams with diverse experiences solve problems optimally.
Professional credentials count. Top candidates have more than great job experience. They'll have presented at CHI or UPA, or they'll show you published articles in journals or magazines, or they'll have earned a degree in the field. Prospects with these credentials keep up with their peers and stay aware of the latest relevant research. Their knowledge of theory helps them anticipate issues before they happen.
Ask for cheerleading and negotiation examples. Whether you work with consulting clients or with an in-house development team, usability work depends on persuading folks to do things your way. This is a great opportunity for prospects to impress you with specific stories of how their communication skills carried the day. If they can't convince you of their skill, how will they win over people at work?
Can you imagine working with this person? When evaluating coworkers, people tend to find social skills are more important than job skills. But a job interview is an artificial situation, so awkwardness abounds. At my company we make a point of taking candidates to lunch and just chatting with them.