As an attorney who specializes in collector car fraud there is no way to stop it. With the values being what they are, there will always be folks trying to get more for their car than another car. The extent to which they will go is anyone's guess.
As far as advertisements go, most people don't realize it, but they can be held to whatever they write about a car. If they state that a car is an L78 or Z28, then they can be held to that statement if the car turns out to be otherwise. A carefully worded ad may even be deceptive. The best practice is not to rush into any purchase and do your homework ahead of time. Even that is not failsafe, but it certainly helps flush out the less sophisticated frauds. Also, I highly recommend having any Camaro looked at prior to purchasing, by someone such as Jerry MacNeish to ensure what you are negotiating for is really what is being offered.
Also keep in mind that if a deal is "too good to be true" it probably isn't true!