I don't see how doing a compression test on a motor out of a car is even possible. Sitting there with an impact wrench on the crank pulley bolt is not the correct way to spin the motor over. Its just going to snap the bolt or strip the head if you use a very powerfull one. Trying to turn a motor over with a impact sorta defeats the impacts purpose.

Even if you did, the motor would turn so slow your compression reading would be crap.

Leak down test is a different story, would much rather recomend that.

If you buy something and cant see it run, plan on rebuilding it. Its not that much to have a machine shop do a little work, and new NPR pistons, bearings, and rings can be had for pretty cheap. Lots of stuff can be reused one reconditioned or inspected at a engine shop.