Never buy a German car out of warranty. If you do, make sure you get a VERY good PPI, to understand what you are getting yourself into.
Also given the choice between a $9,000 Merc that is nice but may need a few things over time, and a $14,000 Merc of the same model that is immaculate and dealer/specialest maintained, ALWAY go for the more expensive one. It will cost you less over the next 12 months. Not that I know from personal experinece.