I want to trade in my MB with enough time and miles left so that the dealer can turn around and sell it as certified. What is the max miles it can have and max years old that the car can be?
You are in an interesting situation. As much as I like MBz, it is not a brand that I would buy a newer example of without a warranty of some length in place. That being said, doing what you propose will probably not provide you with a lower net cost for your new car ("price" minus "trade-in"--both of which are variable) than if you could find a buyer for it yourself and then go in and "clean deal" a new car. What it will provide you with is the knowledge that you can definitely get rid of your old car quickly and when you want; something that an MBz with a near-expired factory warranty may not provide in the private sale market.