The CPO warranty from a Mercedes dealer is indeed a vert strong warranty, honored at any MB dealer in the US. In a sense , you paid for it, but is worthwhile. They will fix it. IF it repeatedly has problems, they will address them MB does not want th CPO program to fail. Perhaps you can cover your bases a bit by having a calm chat with the General Manager of the store, or at least the Service Manager; express your concerns and get him involved in making sure that this car is right.