The oil stains tell a story, I've never sold a car, they die in my hands, but they live on in the manuals, I can leaf through them and see the skinned knuckles and hear the swearing written in greasy fingerprints, 'ah yes', I think, the time that the clutch slave-cylinder pushrod broke through the actuating arm and I spent two days on my back in the snow. Therein lies the entertainment.
The re-written procedures tell stories as well. My Alfa GTV manual (many oil stains) has the section on cam chain timing crossed out, and the words "don't ever do this again" written in its place. Stapled in is my re-written procedure for actually getting it right. That mistake cost me £300 when £300 was real money.
On the shelf I have:
Land Rover Discovery (bought in a emergency when I had to fix a lucas hot wire ignition system by the road side)
Land Rover Series III - actually a rubbish manual, the proper land rover one is much better)
Daimler Sovreign Series II - again rather poor, the real manual is a god send
Vauxhall Astra (mums old car)
Alfetta GTV (heavily edited).
These days I have an old PC and screen in the garage with the docs on PDF. Oily keyboard, but easy annotation and clean pages.