Interesting read.
But the main thing when buying a second hand car is everything can look all hunky dory with the inspection and the test drive etc etc. The ugliness only starts popping its head out after a couple of months driving the car. You will never truly know what you are getting. And no seller will give you a car to testdrive for a month or two.
Paid some school fees on this topic, specifically on my wifes E46 320d F/L - looked like an awesome buy - until the engine started rattling erratically after about 4 months in. Serpentine Belt was jumping so I knew it had to be something in that area. Was busy replacing part by part and eventually turned out to be a pirate Crank damper pulley. OEM replacement and haven't had rattling issues since.