Men with cold blue eyes and thin faces should perhaps avoid a career selling used cars or life insurance.
New research suggests such features are viewed as less honest than brown eyes and a broad smile.
Scientists asked volunteers to rate photos of 40 male and 40 female students for trustworthiness.
The found that eye colour had a big effect. Brown eyes were generally viewed as more trustworthy than blue, in both men and women.
But for men, it was the coupling of eye colour and facial shape that was important.
More rounded male faces with bigger mouths and larger chins were perceived as more trustworthy than narrow ones. In women, facial shape was not such a crucial factor.
When participants were shown photos of identically shaped male faces, both eye colours were seen as equally trustworthy.
The researchers, led by Dr Karel Kleisner from Charles University in Prague, Czech Republic, wrote in the online journal Public Library of Science ONE: "We concluded that although the brown-eyed faces were perceived as more trustworthy than the blue-eyed ones, it was not brown eye colour per se that caused the strongest perception of trustworthiness, but rather the facial features associated with brown eyes."
A total of 238 volunteers were asked to rate the photos online using a 10-point scale of trustworthiness.
On the whole, female faces were rated more trustworthy than male faces.
Untrustworthy male faces tended to have small blue eyes, distant eyebrows, angular features, long chins and narrow mouths.
"It seems that relatively smaller eyes and a smaller mouth, with downward-pointing corners, are the facial traits that cause the lower perceived trustworthiness of blue-eyed males," said the scientists.