As long as the place has a good return policy (Amazon/eBay cover buyers really well if they go through the supplied channels), or you buy directly from an individual that doesn't sound suspicious (someone telling you up front that it was a mining card is more believable than someone with 120 RX480s that says they were only used for light gaming lol), you should be good. eBay buyer protection in particular is basically bulletproof. As an eBay seller, I can tell you from experience that I just have to account for scammers despite running webcam when I'm packing/sealing/shipping. I no longer sell Apple products or more expensive items on eBay, due to "seller sent me X, wrong item, give me money back", while keeping the good item I sent them. Last straw was a $1500 Macbook Pro a few years ago, near mint and full AppleCare, etc. Buyer claimed i sent him a phone book (coincidentally the picture he sent as proof showed a different box/shipping label and a phone book from his city 1800 miles away from me lol). eBay support didn't care, despite 100% positive feedback and years of good standing they debited the full amount from my account and let bad feedback stand. Of course the buyer had literally two previous transactions and vanished about a week later, probably having screwed over a number of other sellers before they moved on to another strawman eBay account.