2009 with only 18K miles? Nice find!
No defects/problems reported en masse on this model. Solid build. You're probably good to 'buy and drive'. But if want to be certain, bring to MB dealer and have inspection done. Will cost you, though you now have dealer's stamp all is fine. If problems do come up in near future, you have some leverage to get it fixed with no/little cost.
With that said, also suggest you go to dealer for routine services. Shows you care about your car, and builds a relationship with the dealer. Dealer can be your best friend if/when car should do bad things.