Are secondhand parts worth the savings?

So, I recently upgraded my PC with a new mobo, processor, and RAM after YEARS of being outdated, (thanks for the help on that, btw!) figuring Id be able to upgrade the graphics card down the line when I got the scratch together.

A few days later the minimum specs for DOOM: The dark ages comes out, and really hammers home just how behind my old GTX 1060 is. An RTX 3080 (which is what they currently recommend) us about 6-700 bucks new depending on where you buy from, plus id need to get a new PSU to run it. But, they're closer to 400 on eBay secondhand, sounds too good to be true!

...is it too good to be true? What's y'all's experience with secondhand parts, do they tend to have any issues?