I was curious so I went and took a few security guard practice tests online. The worst score I got was an 85%. They're mostly basic questions about taking notes, placing people under a citizen's arrest, when it's appropriate to unholster a weapon, whether or not you should impersonate a cop, or fire extinguisher use. I genuinely think the only way to fail is if you're answering blatantly wrong questions like "shoot him in the face" or "scream at any teenager that approaching on your side of the street is a felony" or "tell them that you're a police officer and will arrest them" or "throw the fire extinguisher into the fire."