Back in the days this car was delivered, there were some pretty common cases of fuel from the CIS injection system leaving deposits on the valve stems and poppets, which ultimately led to a crushed walnut shell treatment to clean it up. This was done with the head on. He may have meant a service to do something like this. Today's fuels have an additive to preclude the deposit problem altogether, and you can add some concentrated stuff with Techron (a Chevron product) to address the situation before it affects driveablility.
Also from around the vintage of this car, MB had some problems with valve seals. These can also be replaced without taking the head off. I don't think it is a 40,000 mile event you plan on though.
So, there may be an explanation along the lines that the guy isn't the most articulate individual in the business, but isn't a complete moron or a devious mechanic. But then again, he could be interested in the car too, as I think the price for one in great shape with such low miles is likely to be significantly higher than $8k in most instances.
Have the car towed to the MB dealer and have it checked out, with a compression test to find out if the car is really in that good a condition. 70,000 miles is hardly broken in, but if it has been sitting for a while it may need some work to bring it back into condition for daily use. If the car is decent sounds like a steal. Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)