Used Chevrolet Engines

I'm looking to buy a used Chevrolet engine but feeling a bit cautious. I’ve seen plenty of listings used Chevrolet engines for sale online, but how can I be sure I’m getting a good deal? What should I watch out for when buying a used Chevy engine?
If anyone has advice or has bought a used Chevy engine before, I’d really appreciate your insights—don’t want to make a costly mistake!
Thanks

Well I'd look for a low milage look in the oil filler in the valve cover to see deposits cleanness of and look at the coolant fittings looking for rust and corrosion the hardest part how long the motor sits can get rust in the cylinders would need a bore scope to see that