The researchers showed a series of ads to 18 patients with damage to the vmPFC. Some of the ads were deceptive (and contained clues to that effect). For instance, one ad for a (fictitious) product named NatureCure described a 'natural' pain reliever that supposedly provided headache relief "without the side effects of over-the-counter pain relievers." But a disclaimer at the bottom of the ad noted, "This product can cause nausea in some consumers when taken regularly."
The patients with damage to the vmPFC proved twice as likely to believe the deceptive ads, compared to a control group of people who had damage to other parts of their brain and a group with no brain damage.
At the end of their article, the researchers point out an interesting implication of their study — that skepticism and doubt require far more mental work than belief:
The article doesn't discuss the legal implications of the study, but I wonder if it might be helpful in cases where courts need to determine whether someone is no longer competent to manage their own affairs. For instance, middle-aged children often become worried about their elderly parents falling prey to scammers, and so they try to acquire guardianship over them. However, current legal tests of mental competence tend to focus on things such as arithmetic skills, not gullibility. So a test that could demonstrate deterioration of the vmPFC might have relevance in objectively assessing if guardianship is necessary.