CPO is an extended warranty program, that is all. The dealer can CPO a car or not, depending on market conditions and condition of car. It costs the dealer around 2 grand but is depenent on the mileage and age of the car. In order to get CPO, there is a checklist that a mechanic must go through to "certify" it, but really what is happening is BMW is making sure that they car doesn't immediately require repairs, so that they don't have to pay out a bunch of money at CPO inception.