Doesn't it bother you to buy someone else's stuff??? I am always a little hesitant to buy something used and get stuck with a bad purchase.
My short answer is "No". It's about knowing something about what you're buying. (Knowledge comes from "research" and "experience", I'd argue in equal parts, but extremes in one can compensate for deficiencies in the other.)
As is it with beauty, "value" is in the eye of the beholder. I have a server platform, with SOLID server grade hardware (ECC, dual Xeon's, 32GB, Passmark CPU score of +14K, 6 drive expander, a perc H200 flashed for IT) that cost me less than $300, with used upgrades, delivered. Can you get stuck with a bad purchase? Sure. On the used market, my mantra is "Buyer beware" - it's a calculated risk. Knowing the risks, the trade-off's and the potential for value gained, is all part of the "dance".