Ive yet to have zero problems buying a used or refurb card. I HAVE recently however, had problems with my NEW XFX RX 5700 XT, for I got a dead one the day I installed it, for the screen went total black and never came back on when the driver said screen may flicker installing display driver. Then when I got my other card from them, it installed with no problems at all, and worked great for about 2 weeks, then started giving me a black or green screen resulting in rebooting my pc. Then I got that and artifacts on my bios screen that would go away if I hard shut down and restarted again, but would still random green/black out and restart my pc, with the artifacts again. Then it finally gave artifacts all the time in bios and windows, and no matter how many times I would shut it down and restart, the artifacts wouldnt go away, to the point I had to rma a 2nd one, and this time I was sent a brand new card in oem box, with seal still intact, and have yet to have, while knocking on wood, no problems yet.
It wasnt a driver issue with the last 2 because the one would black out once it said installing driver, and I tried it with 4 different drivers, and 2 pc's with the same results, and the 2nd card installed just fine with the driver I tried when I got it, and from that point till it finally bit the dust, I didnt update the driver, or any drivers on my pc for that matter, or change any of its hardware, just went south over time.
So needless to say, will no longer buy xfx stuff because of this, new or used. Ive had 3 used RX 580 units, and still have one of them still, and havent had a single problem with them, or my used GTX 1070/80 cards, and my son is still using my 1070 on his rig now for almost a year with him, with no problems that I actually got used, very cheap, that supposedly had no display, and was ready to bake the card when I got it, but worked just fine when I got it, and has since.
So new, used, refurb, there is always a chance, but Id take a used card however over a refurb, as long as its listed as working with no problems, over a refurb that there is a higher chance that it may not work at all, or for a short period, unless it come with a min of a 6 month warranty.