The average entrepreneur spends more time with her employees than she does with her family, so it pays to hire the nicest ones you can find, right? 

Not necessarily. New research suggests habitually pleasant people may not be as deserving of your trust as their more curmudgeonly counterparts.  

Highly agreeable people are more willing to cause harm in certain situations than those rated less congenial, according to a study published in the Journal of Personality.

The researchers imitated psychologist Stanley Milgram's famous experiments from the 1960's, in which he tested participants' willingness to hurt strangers by doling out electric shocks. (The "victims" faked their reactions, and were actually unharmed.) 

For the new recent experiment, the study's authors set out to learn the social personality, personal history and political leanings of their own participants, 35 men and 31 women. In the eight months leading up to the tests, the researchers conducted interviews with the them in order to get to know them better.

When they compared their personality trait assessments to how the individuals behaved during the experiments, the researchers uncovered a counterintuitive finding: "conscientiousness and agreeableness" were associated with a willingness to administer higher-intensity electric shocks to a victim. 

The study's authors concluded that the nice guys were more determined to obey the rules of the experiment than they were to speak up about what they really thought was right.

In spite of the views of people like Y Combinator's Paul Graham, who recently wrote that "Mean People Fail," the idea that niceness can be more vice than virtue in a business setting has its share of influential proponents.

Adam Grant, author of the book Give and Take: A Revolutionary Approach to Success argues that in order to assess whether someone might be harmful to your organization, you have to dig deeper than their outer veneer.  

Grant separates the world into two different categories: givers -- people who are generous with their resources -- and takers -- those who always try to get as much as they can out of others. After years of research, Grant reached a similar conclusion to one in the recent Milgram study: disagreeable people, specifically disagreeable givers, are less likely to do harm. 

"Disagreeable givers are the people who, on the surface, are rough and tough, but ultimately have others' best interests at heart," Grant said at the Inc. 5000 conference in October. "They are the people who are willing to give you the critical feedback that you don't want to hear -- but you need to hear." 

Of course, identifying who's who isn't easy, especially if you have to make a quick judgement during the hiring process. 

Grant's best advice is to get a reference from your job candidate's peers and subordinates, since they're the people most likely to have seen that person's true colors.

"Every agreeable taker can line up powerful people to say nice things about them," Grant said. "It's actually those peer and subordinate references that give you more meaningful data."