What kind of documentation for used engine would satisfy you?

Here's some food for thought.

Four years ago I bought a '68 383 big block and 727 from a good friend that ran good with good oil pressure etc.
He had it on his run in stand and checked it out without me hearing it run and I took his word for it.
It sat in my heated shop for a year and I decided to sell it complete to another friend for $1000.
I made the 400 mile round trip to get it and deliver it to him.
He called me an hour later after delivery and wanted his money back because the engine had a lot of water in the oil.
I went back and he showed me that when he took off the oil pan, it had indeed milky oil in it.
I promptly returned his money and loaded the engine up in my pickup somewhat red faced and apologized to him for his inconvenience.
I then went back to the friend that I bought it from and asked how in the world that the engine would have gotten water in it from the time he sold it to me to when I tried to sell it to a mutual friend.
We couldn't figure it out, so I decided to take it apart and see what was up.
As it turns out, the engine had water in it when he bought it and took it on the guy's word that he bought it from that it was good.
I took the oil filter off in the first step of the autopsy and it had oil and water in it......it actually looked like a chocolate milkshake!
And in taking it apart, I discovered that the engine was in perfect shape other than the water in the oil and the mess it made inside.
I did a lot of measuring and cleaning as well as having the heads touched up and resealed and put it all back together again.
It even had a Road Runner/Magnum cam in it with virtually zero wear.
And the cost?
Other than my time and the cost to have the heads touched up, nothing.
My friend gave me a gasket set and helped me do the work.

It all works out in the end and I have $800 plus my time in it.
And as for the 727, I gave it to another friend who is using it as a core (it had water in it too).
He helps me with my cars and lets me use his shop often.

All's well that ends well......