When it comes to hiring the perfect new employee for your business, hard skills are relatively easy to test. Evaluating cultural fit and personality, though more difficult, still boils down to the same gut sense of someone's likability and compatibility that you use to guide all your social interactions (supplemented in some organizations by a formal EQ test).

So what is perhaps the trickiest aspect to gauge of a potential employee's suitability for the gig? Passion.

There's an obvious reason for this: People lie. Admit it, back in your employee days even you did it, too. Just about no one who bothers to put in the effort to show up for an interview, when asked if he or she really wants the job, will respond with a "meh." Every person who walks into your interview room is going to claim to be a monster fan of your company, your industry, and the specific role you're looking to fill. But all of them can't, in truth, be equally enthusiastic.

So how can you sift those who are truly enthusiastic about the gig from those who just think it sounds cool (or even just sounds like a paycheck)? On recruiting blog Fistful of Talent recently, Kris Dunn, the chief human resources officer at Kinetix and a blogger at The HR Capitalist, offered some ways to tell if someone just drifted into your sphere or has actively and enthusiastically chose the type of role you're looking to fill. He suggests the following four questions:

1. How do you stay up to date in the field?

Those with a true passion for the work they do spend time outside the office building their knowledge and honing their skills, so this should be a softball question for the genuinely enthusiastic that gets you a smile and quick, relaxed response. If the candidate can't name any professional or personal development she's done lately, that's obviously a red flag, but it's not the only one to look out for.

"If you see a glut of reliance on professional training and formal activities that happen in company time, you're probably not dealing with passion," writes Dunn. "Passionate people tend to loathe the training in their own field, because they don't think it's deep enough." 

2. What's a big question in your field you'd like to solve and why?

"Ask them what they've done related to starting to figure out the answer," writes Dunn. "Probe hard on the answers they give. See any creativity? You might have passion. See lots of glittering generalities or an emphasis on the work of others? That's fake passion." 

3. How do you find others in your profession to connect with?

Also ask candidates how often they connect with others in their field outside their company and what they talk about with their fellow professionals, suggests Dunn. Why? True passion loves the company of others who are equally immersed in a field. Those whose interest in a subject or niche ends at 5 p.m. are unlikely to bother with this sort of after-hours networking.

4. When have you been most satisfied in your work at Company X?

What's the point of this sort of "motivational fit" question? The answer will tell you if the person is looking for comfort with a culture or a particular work style, or really searching for a place where he can put his passion to work doing a particular kind of job. "If the answers show a consistent theme of talking about BS factors rather than a clear line toward being able to do interesting work related to their field, it's hard to project them as passionate in their field," cautions Dunn.

How do you gauge passion in an interview?