Call me Mr. Cautious if you like, but anyone who lets rust scabs develop in places that are easy to touch in with a paint stick isn't likely to have spent any time keeping the wheel arches and jacking points free of mud/rust etc etc.
I viewed a one owner 190E recently, advertised locally as lowish miles, FMBSH, allegedly pristine etc. Within five minutes I found numerous problems which would have cost far more than the asking price to repair. The car had been "the wife's car" for a number of years, so other than a quick wash once a week and a service every couple of years at the local garage, it had not been looked after at all. The seller (the husband) claimed to be unaware of any of the problems I found. I'd much rather have a car with higher miles and owned by a Merc enthusiast any day. "One owner" might look good in the ad, but it can often mean precious little in terms of condition.