He spoke with a polished English accent, once shared a crème brûlée torte with Hillary Clinton, and spent part of the summer officiating tennis at the 2008 Beijing Olympics.

Charles Carlson gave every indication that he was a student worth watching at the University of Minnesota when he sat down for an interview with the Minnesota Daily, a student newspaper, during the Democratic National Convention in August. Carlson was an at-large delegate at the convention. He later announced his candidacy for the Minneapolis City Council.

“He was a Beijing Olympics tennis official and is a University graduate student, GLBT rights advocate and director of operations at a Minneapolis architecture firm,” read the Daily’s story about him. “Is there anything Charles Carlson doesn’t do?”

This week the paper answered its own question: tell the truth. An investigation published on Monday by the Daily revealed that Carlson had lied about many of his achievements.

There was no communal torting with Hillary, and he didn’t officiate at the Olympics. Carlson grew up and went to school in Minnesota, which meant his transcripts from Phillips Exeter Academy, Princeton University and two schools in England were forged. When confronted with the evidence, he admitted that he suffers from a mental illness for which he was once institutionalized. The English accent disappeared, too.

“I spent six years being a gay nothing that people just made fun of, and then when I was discharged I found out that people would believe anything you told them,” he told the Daily.

Carlson is far from alone in discovering that members of the public and journalists, be they student reporters or veteran scribes, will often take the facts at face value. An old saying in journalism holds that, “If your grandmother tells you she loves you, check it out.” It’s good advice, but rarely followed.

One weakness of journalists is that we’re always looking for the perfect source. When we find someone who epitomizes the trend or subject we’re describing, the feeling is relief, rather than suspicion. Yet one of the best ways to spot an unreliable source is if they offer up the perfect story.

If a reporter comes across someone with a remarkable story—a story he can’t wait to put his byline on—the assumption is that the person isn’t lying, rather than the other way round. We don’t doubt their tale, because it’s not in our best interests to do so. Deadline approaches.

In a situation such as Carlson’s, a series of lies can be made to seem plausible if they are stitched together from a single known truth. In Carlson’s case, he was already an at-large delegate at the Democratic National Convention. That opened the door for him to regale a reporter with a string of fabrications and exaggerations. That he did it with an accent likely made him all the more charming and believable. After all, who would fake an accent?

Journalists are particularly susceptible to what I call the self-interested source, because we need them. Every story requires sources, and there’s rarely the time to vet each of them like the proverbial loving grandmother. We take them at their word, and we get burned. They get their time in the limelight.

The Associated Press was burned in 2006 because it believed a recently deceased man’s family when they said he was the co-writer of “Itsy Bitsy Teenie Weenie Yellow Polka Dot Bikini.” The true author, who was alive and well, was less than amused to learn that this stranger had been claiming co-authorship for years. The deceased man’s family was even more shocked.

The New York Times, Vanity Fair, and PBS were all taken in by a man claiming to be the iconic “man in the hood” whose photo became the signature image of prisoner abuse at Abu Ghraib prison. They all thought they’d found the perfect source to describe the abuse that took place at the prison. After Salon raised questions about the Times story, the paper reinvestigated and published an Editor’s Note:

A front-page article last Saturday profiled Ali Shalal Qaissi, identifying him as the hooded man forced to stand on a box, attached to wires, in a photograph from the Abu Ghraib prison abuse scandal of 2003 and 2004. He was shown holding such a photograph. As an article on Page A1 today makes clear, Mr. Qaissi was not that man.

The Times did not adequately research Mr. Qaissi’s insistence that he was the man in the photograph…

Craig Silverman is the editor of RegretTheError.com and the author of Regret The Error: How Media Mistakes Pollute the Press and Imperil Free Speech. He is also the editorial director of OpenFile.ca and a columnist for the Toronto Star.