Many years ago I experienced a "false negative" event like this: two different people called me claiming to be FBI agents. Of course I laughed and hung up. A couple of weeks later a car pulls into my driveway, two dudes wearing mirrored sunglasses get out, introduce themselves as FBI agents. I ask them to show me credentials, which they do. Lesson: you can just hang up on all calls purporting to be from federal agencies. They will show up in your front yard if they really need to talk to you.
How many people know what [insert federal agency] credentials look like?
I have a friend who is one of the 2k IRS Criminal Investigation Division agents in the entire country. He's full-blown armed federal agent a la FBI, etc.
He tells me it's very common that when he goes out to do an "interview" people say he's not real and they're calling the police, slamming the door in his face.
The local cops show up, check him out, and then go back to the door with him. In his area he (of course) personally knows many local cops and they'll show up laughing "Oh another one, huh?". It doesn't bother him at all and I seriously doubt a scammer/impersonator would stand around waiting for the police to show up and then have the gall to try to con /them/.
Additionally, they have undercover vehicles (of course) but when he goes out for interviews like this it's in the classic "Oh yeah that's a cop car" vehicle with US Government license plates.
