The problem with doing that is you have to know how to lookup specs. You could be buying a 5-10yo PC. Easiest way to tell is search for the CPU (processor) model and find out when it was released.
A few sites to check:
https://www.cpubenchmark.net/singleCompare.php
http://cpuboss.com/
Also better if you're looking for a desktop. If you buy a refurb laptop, it might have broken keys, faded/damaged screen, or other things that are worn out. I bought an 'open box' gaming laptop from Best Buy a while back. It didn't come with the power adapter. So definitely a disappointment to receive it and not be able to turn it on for a few days until I received the power adapter I bought on Amazon. Tech support line told me to return it if I don't like it (and absorb the restocking fee).
those come with a 1 year warranty. I've been lucky I guess and have had no problem. Plus you can return it for 30 days no restocking fee's .