ok,, that is easier even though I have no specific information about the model...
First on a particular car you should check with Carfax to see if there is some record of speedo rollback or collision damage not disclosed or known about by the present owner,
Then check alldata.com and plug that car into their data base and read the list of safety bulletins, recalls and updates which MB has issued... if some look important get the actual copy of the bulletin and read it...
Check the archives of things like ' consumer reports' and 'powers' and any other consumer feedback from owners of those cars...
Then when looking at a particular car spend the $100 and have an independant testing company like LemonBusters run their checklist on the car.. and deliver the results directly to you..
Everytime you can find an owner of the model you desire stop them and get their opinions.... most people are flattered and love to tell their feelings, one way or the other, about their car...

I was saying there is a continuum and my car is at the extreme end of that.... ( the good end ) LOLOLOLOL