This seems to be a scam..

Link:

http://blogs.cars.com/safe/2008/03/carscom-full-pa.html

Cars.com is a legitment websit, but Cars.com is not involved in the payment process of the vehicle. If you receive any email from Cars.com about payment, then this is a scam.  All Cars.com emails will have a cars.com domain. I.e. [e-mail]. If you see any emails with support@car*****illings.com or payment@car*****illing.com, these are scam email accounts.

Please review sample scam emails below.