Carfax presents itself as having a comprehensive report on any used car. They imply that they have access to an in-depth reporting system of cars’ histories. In truth, no such database exists. They have only what they’ve been told, and I’d be surprised if that were more than 1% of 1% of everything about all used cars.
In addition, Carfax will often post “112 complaints about this car” (or similar wording) and require that you pay a fee to see them. When you do, they’re meaningless and often extremely inaccurate. I have no proof, but I suspect that they “populate” the reports with “created” data just to sell the reports. Try getting a Carfax on your own car and you may find it peppered with inaccuracies. In my friend’s case, the model, options, and even he drivetrain were wrong… and the data was so far from accurate as to be laughable. The make, year, and VIN were right, but that was it.
I do not recommend that you use Carfax as a source of information. If a dealer gives you one, use it to light your fireplace.