I, personally, am not rich enough to buy used hardware. Thus, i only buy brand new stuff.
With hardware, one has 2 choices;
1, Buy from questionable source, no-name hardware and play the lottery that you MIGHT get decent piece of hardware for paying peanuts.
Buying used always has it's risks and getting working hardware is 50:50 chance. Either it works and you scored a great deal (hence why people buy used hardware in the 1st place, to get great deals), or it doesn't work (or works partly) and you have a nice paperweight. Not to mention money wasted + your own time and effort troubleshooting it.
2. Buy from reputable source, brand name, brand new hardware, get warranty, be assured it works, while paying proper price for it.
Since used hardware is sold "as is", there is 0 expectation for it to work like brand new hardware. Nor is there any warranty with used hardware.
Due to this, for myself, the price of used hardware is instant 50% off from MSRP. And i don't care if the GPU is "open box", "almost new" etc. If there is no warranty with GPU, 50% off from MSRP.
As for my own old hardware, i haven't actually sold anything. I've kept most of it around (since i have more than 1 desktop PC) and i can use it in my other PCs or keep it as redundancy. Though, i have donated some of my unused PC hardware to the charity (one PC case + several case fans). And when time comes, i may donate more. But storage drives i have, will be seeing full/deep format + shredder.