certified means it has no major mechanical defects they noticed (the prep work takes 10 minutes tops, and is a basic safety inspection, and if the car falls under a mileage limit it is then certified) car fax will miss many things, I had a civic that came back with a salvage title 2 years after I bought it, and the dealer and I both ran a car fax (title had changed hands 5 times prior to the dealer getting it, and at that time the title looked good, later got a letter from the state stating they messed up)
