A couple of things I would mention here....
First off, ideally I agree with much of the above, and particularly the part about not rewarding the miner with a subsidy on (their) loss. But, putting the emotional kick on hold, let us discuss it a bit.
Is this person near enough to you to be able to meet, see it working in a system, and run some tests on it?
Basically, I would not purchase if the above cannot be dealt with. This card could well have a VBIOS flash that would have made it run better for mining. In this case you would want the "regular" VBIOS to be reinstalled.
After that, I would want to put it into a rig and run a couple of HARD video benchmarks on it. In addition to that, I would also want to install Afterburner and see how much overhead it has left for an OC on both the GPU and memory. As this is going on, check temps on the card as it relates to your ambient.
Mining is rough on a card and very likely that its lifetime is shortened as a result. Hard core gaming (can) do the same. One never really knows how long a graphics card will last. I have had some go seriously long times, but of course mining wasn't a "thing".
I would give this serious thought based on the above circumstances being possible. Make sure to visually inspect the card as well. Stripped screws? Dirty heat sink, and so on...
If it actually works and lasts even a couple of years at 80-90% of its capability I would still call it a deal. Do I recommend doing so? No.
Edit- one other factor here is the PSU requirement and space. If you don't already have that covered I would put that a strike in the no column as well.