In Most Wanted Vol. 1, the villain Trickshot has Heightened Charisma: +10. He also has the weakness Reduced Charisma: -7. This is the only time I recall seeing a hero with a heightened and reduced ability in the same category. The sections on his background and personality explain the dualism, saying: "Trickshot worked as a MEDUSA operative for a time before his rebellious nature made it impossible for him to keep following orders. ... Trickshot is rowdy and rebellious. He loves displaying his talents, gathering a crowd. He is a how off with a big ego."

Alone into the Night gives the anti-hero Night Raven the weakness Low Self-Control due to his uncontrollably violent nature. The module also gives him Lowered Charisma: -7 due to extreme motives for true good. Now fifth level, Night Raven has been playing the part of a criminal for most of his career, so I interpret his lowered charisma as a culmination charisma penalties rather than the "reduced charisma" weakness.

Here are recommendations for charisma adjustments that appear in other modules. This not a complete list.

+1 point of Charisma for stopping an armed crowd of emotion-controlled convention-goers without resorting to violence (optional, along with bonus xp; Great Iridium Con).

+1 point of Charisma for rescuing two bystanders trapped at the top of a Ferris Wheel when a battle breaks out at the circus (Organized Crimes).

-1 point of Charisma if assassins succeed in killing a man who the players were specifically assigned to protect (Honor).

As a closing note, my favorite example of a villain with below-average charisma is Rocket Ma'am from Opponents Unlimited. Her charisma is 8, listing her with +2 reactions from good and -2 reactions from evil (per standard rules). In her case this makes half-sense. During the day, she works at a police station, and because of her job she often isn't available to accompany her teammates on capers.