Let's be sensible here
Every car worth less than £1k, by very virtue of the fact that it is inevitably either really quite old, really quite crap in general or any combination of the two could have a multitude of things wrong with it.
A £20k Ferrari falls into the same bracket - it is entirely possible it has a catastrophic fault. I could buy a £20k Ferrari, I would be no more able to realistically fix it properly than someone buying a car for a few hundred quid.
If buying privately, expect and inspect for the worst, it really is that simple.
Acme has absolutely no idea what's wrong with his car other than it makes a noise. If I drove it I might think "hmm what's going on here", it wouldn't necessarily stop me buying it for £400, if would definitely stop me buying it for £20k