IMO, there is way too much confidence placed in carfax. Not everything that has happened will show, and it certainly guarantees nothing. Franchised dealers will not sell a vehicle that has had major structural damage, been underwater, is salvaged, and in rare cases, if they do, the laws are very strict about disclosure. In otherwords, they must tell you. You can be pretty confident that a business license worth millions of dollars, is not going to be jeopardized by the lack of this disclosure. There is too much to lose for the dealer.
BTW, I'd do a Carfax report on a private party buy, or one bought from an independent used car lot.