My parents bought my 1985 300D Turbo for $3000 on ebay (wihtout driving it or seeing it in person first). In retrospect I think they got ripped off since the car has some ugly dings and dents (and two 3 cm holes from where they pulled the dent) towards the rear. I do love the car but honestly don't know why they paid so much for a 192,000 mile car with some nasty dents (although no rust, CA car). The interior however is damn near perfect (no cracks in the dash), MBTex seats with no tears. Although the driver seat is a bit saggy, the car still fits me like a glove, with the huge steering wheel, huge arm rest...just a comfortable car. The factory white paint still shines, but there are of course paint chips at the front from pebbles and such.
Anyways, it also drove like crap at that time. My father's experience on the whole matter is that he wouldn;t have bought the car if he had driven it first. Although the compression is very strong, i assume, since the engine barely cranks at all after the glow plugs do their thing (or is it that someone simply messed with the timing?), it simply needed an ALDA adjustment. The alda adjustment wasn't performed until 1.5 years later, which is sad because we all assumed it was supposed to be that slow since it's a diesel. The tires were crappy no names which were replaced with michelins when the cords started showing. My parents told me the dents were listed but not nearly as apparent in the photographs as they were in person
It also had some vacuum leaks which caused the transmission to shift pretty damn hard especially in first gear (or 2nd rather?) We spent some money to get the vacuum leaks fixed and got some new tires and shocks, though the crappy green coolant is still in there.
To conclude, my parents never actually regretted the purchase; they wanted to get me a safe car to learn to drive in and they certainly succeeded. And now that we got it running well, we're all pretty happy with it.