One thing I pride myself on, Jafar, I'm an excellent judge of character.
(Iago: Oh, excellent judge, sure... NOT!)
~ The Sultan
The guy I bought the drugs from seemed like a real straight shooter!
~ Alan Garner about a drug dealer who sold him roofies instead of ecstacy

These are heroes who have a bad habit of trusting the wrong people. These characters tend to be either very gullible or simply too quick to trust, and often land themselves in tight spots when the inevitable betrayal comes.

One prominent example of this category is Inspector Gadget, who frequently mistakes the henchmen and minions of his enemy Doctor Claw he encounters during his assignments for "friendly" characters, often nearly getting himself killed as a result.

Fortunately though, not all of these characters are extremely foolish nor highly gullible. Some of these heroes are still able to detect malice from those that they trust and try their best for counteract the unwanted consequence of their actions. Nevertheless, these attempts are not always successful.