Carfax is but one tool a consumer can use.
KBB etc that provide valuation based on vehicle condition miles etc, is another.
When you use the two together, the valuation is provided based on the condition and accident record of the vehicle. Together, along with other things, allow the consumer to be more informed.
The fact still remains, vehicles that have been involved in an accident, are typically valued at less than ones that have not. If the consumer wants to ignore that, or over look it because he/she loves the vehicle, that's their prerogative.
Mike