Calling potential buyers "fools" for using carfax or other services is nuts.
How terrible that someone would want to do a little homework on what they were going to look at. Verify if the equipment mentioned in the ad is correct or that the car isn't a insurance wreck, etc... I will state it is not the be all end all of determining whether a vehicle is good or not, but with the information from it, you can piece together some type of history. Where its been sold, registered, usage, etc... The buyer is going to get the VIN if they look at it. Withholding it from them just makes your buyer pool even smaller.
In my last used vehicle purchase, that turned up two vehicles in my search that were rentals out of the northeast, had accidents, and when I looked at one of them, the repair work was easily spotted in the area noted.
As for someone calling the cops because someone won't supply a VIN, well, I don't know that even dignifies a reply.