Something sold at a price favorable to the buyer. As soon as you sign the check and drive it off the lot you own a used car. Granted if no one ever bought a new car there would be no used ones, but that's not going to happen. Be it gas or diesel, Mercedes Benz enjoys one of the lowest depreciation rates in the industry. Some models hold their own year after year.
Safety is a another factor to take into consideration.
Mercedes has consistently ranked at or near the top for as long as government and industry have been running crash tests. As for service, don't let anyone fool you. Long term maintenance costs are no greater than any other comparable automobile. If you add it all up it just makes good sense. The quality, value and safety are there to had in a used Mercedes Benz.