With this mileage the first thing I would do is contact the seller and ask about maintenance history and see if any major items done already. E500Es are well built cars and very rewarding drives provided they're not neglected.
Aside from regular maintenance check if the following has been addressed:
Top and bottom wiring harness
Engine/gearbox mounts
Timing Chain, or rails/guides at least
Gearbox rebuild or proof of regular fluid change at least.
Rear struts and Spheres
ETA/MAF/EZL
If the above has been taken care of then I would go and look. If not I wouldn't bother unless you have deep pockets. It's about 150kmiles onwards that these require attention and replacement. And this is big money! This is not reflective on low miles E500Es as such but will eventually fail, and again this particular example being at 200k is nearing these big item failures if not already done.
So if our german friend is accommodating and that he/she is able to prove money spent on the beast, then go and view. Aside from the usual comestics/rusts which Bill pointed out check the following:
Under bonet -
Pull back sleeve on wiring harness or check date code
Oil weeps/leaks around the Cam magnets/valve covers/hose under PS reservoir
Air/smog pump operation - can be noisy at initial start up.
Washer reservoir - check for leaks around pump and operation
If you can get underneath you might discover plenty of oil leaks -
check oil cooler hoses, trans and engine ,
tandem pump seals
Steering box
Usual gasket sump and trans front seal/sump
Rear Hydro struts leaks
If you can drive it , drive it hard and take it on autobahn making sure it downshifts at full throttle and redlines . If it hangs before 5000rpm not good. ( already I can see from photos ASR light is on ?) Check reverse engagement if severe delay (+3seconds) and your hear clicking then it's due for a rebuild. Monitor coolant temp , if it hits above 100c this time of the year or while sitting in traffic the fan clutch could be knackered.
Remember the car is 20+ years old and the mileage reflects this , which basically means it's been driven as it's meant to since they're so addictive.. But they do require a lot of maintenance , almost constant I would say.
Hope that helps!