It's a wise suggestion not to put more faith into a Carfax report than it merits.

One can't really know before seeing it if the Carfax report for a particular car will be worthless. It sometimes does turn up useful information, e.g., that what's being billed as a "southern car" spent its first 15 years in the rust belt, that a vehicle has been through the hands of several short-time owners in the past couple of years, that it's been through one or more wholesale auctions recently, that it's been involved in reported collisions, etc. - and sometimes real show-stoppers. When available, that sort of information can really help when initially trying to feel out a prospective car from a distance when one can't conveniently lay eyeballs on it, kick the tires, etc. When it gets serious, you're spot-on - a good PPI is a necessity.

Where a lot of folks get into trouble is when they assume, just because nothing bad shows up in the Carfax, that nothing bad ever happened to the car! It's an attempt to turn a lack of information into information - a failure to think critically.

Naturally, Carfax doesn't have much interest in emphasizing the inherent limitations of the information they can provide!