Very little weight should be given to a CarFax report. These reports seldom have maintenance or repair histories and are frequently wrong.
CarFax is a business venture designed to make money by convincing people that their report is the final word on the history of the vehicle and CF has done a pretty good job of promoting their plan.
Dealers use it for the same reason. It’s a sales tool to aid in selling the car; nothing more.
Wonder how much money CF has coughed up on their guarantees… 
http://consumeraffairs.com/automotive/carfax_unltd.html
http://www.consumeraffairs.com/automotive/carfax_inacc.html
http://www.consumeraffairs.com/automotive/carfax_ads.html
http://www.consumeraffairs.com/automotive/carfax_sellers.html