Is Carfax really all that reliable?

I was thinking about this because of a question asked today about issues with a used car and the prospect of possibly buying a new one.

I can’t tell you how many times I or someone I know has been in a fender-bender or even something a bit worse, only to drive off and not report it to the insurance company.

If so many people do that to avoid their premiums going up and just paying out of pocket for repairs, how can something so trumpeted as Carfax be anywhere near as accurate as they claim?