We've been through the rise and fall of cryptocurrency mining using GPUs several times now—first in 2011 with Radeon HD 5870/5850 cards and Bitcoin (SHA256), then in 2013 with Radeon R9 290X/290 and Litecoin (Scrypt) and other alt-coins (X11, X13, etc.), and now we appear to be nearing the end of the Ethereum (Dagger-Hashimoto / Ethash) craze—maybe. Historically, the mining boom and bust leads to many formerly ambitious miners deciding it's time to pack up camp and sell their equipment. That can be good news for gamers looking to pick up a relatively cheap used graphics card, but it raises an important question: Do you actually want to take the chance on buying a used GPU that's been mining 24/7 for many months?
Let's step back a bit and first talk about what sort of deals you should be chasing in the first place. The way I see it, anyone looking for a 'deal' should never pay anywhere close to MSRP—that's not a deal, it's what you should expect to pay given sufficient supply. So when the RX 480 8GB initially launched with an MSRP of $239 last year, but it wasn't readily available for less than $280, I didn't think cards priced at $240 were a great deal—it's what we should have had all along. In terms of current generation cards, the official (at launch) MSRP of the RX 580 8GB is only $229, the RX 580 4GB is a $199 card, and the RX 570 4GB is supposed to cost $179—prices which you'll never find right now. Similarly, GTX 1070 cards should start at $349, GTX 1060 6GB at $239, and GTX 1060 3GB at $199. If only, right?
For gamers, I see little point in jumping on the bandwagon at the currently inflated prices, because give it a little time and we're guaranteed to see lower prices. The cryptocurrency craze can't last forever, in part because the algorithms are designed to slow down the generation of coins by increasing the difficulty. Even if Ethereum goes back to a $400 price point, the difficulty will increase until it reaches a relatively stable equilibrium. In the past, that usually means the break-even time for new computer hardware used for mining will be around 9-12 months, instead of the 2-3 months we've had in May/June.
If you're wondering about the 9-12 months timeframe, my experience is that GPU miners become hesitant to put a lot of money into new hardware when it will take nearly a year to recoup the investment, and the reason is simple: 24/7 mining puts a serious strain on the graphics card components, so after a year or so of constant use a lot of the cards will start to fail. Fans wear out, VRMs fail, and RMAs (if you can get them) take weeks to complete. The point is to make money, not just break even, so if you start replacing cards after a year then you may not realize much of a profit—particularly after power costs and other expenses come into play.
Combine the above and buying used graphics cards starts to look like a gamble. You might be able to get warranty service, but I've personally had a couple of tier one companies deny claims based on burned out capacitors. "You did something to destroy the card, causing physical damage, so you're on your own." But the age of a graphics card is also a factor—something relatively new like an RX 570 or RX 580 can't possibly have been used for more than a few months, and if it's still working right now, you'll probably be okay for gaming purposes.
There are also plenty of miners that aren't running their GPUs overclocked to the max, and in fact many will undervolt/underclock to reduce power and improve longevity. Others may underclock/undervolt the GPU core but overclock the VRAM, as Ethereum is more sensitive to memory bandwidth. Unfortunately, it's entirely possible to damage GDDR5 chips while leaving the GPU itself unscathed. Anyway, a card used for mining might actually be in good shape... but there's unfortunately no way to effectively know what a card has been through. Cards that are "100 percent tested and working" may work great, or they might crash at the first sign of a heavier workload. So again, it's a bit of a gamble.
If you do find a good deal, be sure to run some gaming stress tests as soon as the card arrives. Unigine Heaven, 3DMark Time Spy, or any demanding game would be good. If you experience any crashes within the first few days, immediately demand a refund—and only buy used cards that offer a refund, unless you're willing to attempt repairs on your own.
What used graphics cards should you look for? My advice is to stick with the latest generation of AMD and Nvidia GPUs. Anecdotally, Nvidia cards tend to be better about not dying under intense workloads—though there are always exceptions—so I'd be slightly more inclined to buy a used Nvidia GPU. For the current cryptocurrency mining boom, the RX 470/480/570/580 are popular, and GTX 1060/1070 have joined that group. Older cards like the GTX 900 series and AMD's R9 300 series are still viable, but those are two years old (or more) and generally use more power for equivalent performance while lacking newer features, so I'd skip them.
Of course, all of this talk of used cards is only meaningful if the price is right. Individual definitions will vary, but for me that would mean around $150-$180 for a used GTX 1060 6GB or RX 480 8GB (basically 25 percent off MSRP). Anything more expensive than that and I'd rather take less of a risk and just buy a new card, after prices on new GPUs to return to normal. I'd also be careful with any used graphics card that's more than a year old, unless you get a really good deal, but those are mostly previous generation hardware regardless.
Here's the thing: I don't think we're likely to see used cards get down to prices like that any time soon. Because even though mining is a lot less profitable now than it was in May and June, it's still doing okay. You can check places like WhatToMine or use the NiceHash calculator to get an estimate of the current profitability, which say that RX 480/580 8GB can still net around $1.50-$1.80 per day. Miners will still likely pay up to $350 for that level of income, sometimes even more. That's why graphics card prices are still higher than MSRP, and no miner is going to sell a card for a song if it's still working properly and earning $1.50 per day.
For now, a quick search on eBay shows that even used, RX 480 cards are still going for well over $300, and RX 580, RX 570, GTX 1070, GTX 1060 6GB, and GTX 1060 3GB are similarly overpriced. Given my "don't pay more than MSRP" mantra, that means stay away. When prices do come down, which they eventually will, if you're still in the market for a used graphics card, here's my advice.
First, don't buy a card if you're not allowed to return it for a refund. Second, pay close attention to the fine print—some unscrupulous sellers are trying to trick people into buying boxes, 'tuned' BIOS versions, etc. Check the seller ratings as well, as established sellers are less likely to be fraudulent. And finally, if a deal looks too good, it probably is.