Here's the truth about CarFax.
Example 1:
If you have a stonechip in your windshield and call your insurance company to have it fixed, If they have you get a police report to document it, it shows up on a CarFax report as a minor frontal impact accident.

Example2:
If you spin off the road and snap off a telephone pole, just have someone pull you home. Then you can back half your car with another one that was in a head-on accident. Make sure you do a good job cleaning up the blood and where you spilled your beer on the interior... Throw on a good coat of wax after you've blended the paint job... You're good to go! No accident report, no insurance claim, no CarFax report!

Its a guide to help, but you can't ever be 100%