what qualifes a car to be certified

Cars designated "certified" by dealers are just the lowest risk cars they sell. Newer, lower miles, good history of maintenance. They're mostly lease returns.

I would only buy factory certified cars. Third party sellers like CraaazY Joe's Car Emporium and Taco Bar may "certify" a car but I doubt the cert is worth the paper it is written on. Each manufacturer will have its own set of criteria for what it will certify.