Cars: Value-Add of "Certified Pre-Owned"

[theben]

All,

If I were to go to a dealer and purchase a used car of their make, is there any real different between the "certified pre-owned" designation and none at all?

Hypotheitcal case: If I bought a mercedes at a authorized dealer and both cars were identical in basic stats (mileage, vintage, features, color, etc) but one was "CPO" and one not, is there an actual difference in quality?

Also, what premium does the consumer bear for one of these designations and is it worth it?


Note - one reason I am wondering about this is because I have observed that 50% (or less) of cars get this 'CPO' tag at authorized dealers of the same make. I ask myself why this is the case.


TY