You can pick up older Mercedes diesels for fairly reasonable prices.
We just sold a 2007 E320 with 130K miles on it for $3K, the Kelly
bluebook price. The car still looked great and ran very well most of
the time. It had begun to develop some annoying electronic glitches
however that our mechanic couldn't get a handle on. It was a v6 turbo
diesel that developed 400 ft-lbs of torque and got over 30 mpg. The
fuel range on trips was close to 700 miles. Except for the glitches
it was still a great car that will probably go another 70K miles or
more.
That's more or less what I've been looking at. Sound like your buyer got a good
deal. I wouldn't mind putting a few bucks into it.
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Our buyer was the local CarMax since that is the quickest and cleanest
way to sell that I'm aware of. Since it was over 10 years old they
were going to auction it off, and I doubt that they made much money on
the deal. I didn't want to be bothered with a private sale and
possible recriminations from a disgruntled purchaser.
The biggest issue with older luxury cars is maintenance. The cars may
be a bargain but parts and service are not.