True, Carfax don't know what they don't know. Remember the furor over flood damaged cars from Louisiana in the used car market in the wake of Katrina in 2005?
Those that weren't scrapped were marketed as used, maybe with salvage title/salvage certificates, maybe not. I recall consumers gave Carfax a lot of heat over that, often fueled by consumer reporters at local TV stations that fixated on the story. Carfax info. is only as good as its sources. Even an educated buyer that does due diligence on a vehicle purchase isn't assured of a good purchase if the seller didn't comply with the legal requirements of their state on this issue.