Advice on buying junkyard engines?

#1 look for engines from front-end wrecked vehicles. You know they were likely driving when they died.
#2 don't buy engines from rollover vehicles. Oil starvation is a *****.
#3 grab the water pump shaft and give it a wiggle. If the water pump is crap, so is the motor.

This all assumes compression and leakdown check out ok.

I have a Neon at home with a piston slapping. Didn't find the water pump was shot until after the motor had been at home for a year waiting to go in. I had no choice but to gamble, and I kind of lost.