Like other members have already suggested, a proper full PPI report is your best friend. There have been many cars that looked clean on the outside, but had some hidden issues. In case you do end up purchasing the car, I've attached a link to our site's DIY tech articles on the car ( I know that the article says it's for the C Class, but mechanically the cars are the same) - they'll save you a ton of headaches and $$$. Best of luck!

Mercedes-Benz C-Class W203 (2000-2007) Technical Articles – C320 E320 ML320 CLK320 SLK320 – Pelican Parts


-Dmitry