If it has no brand, like no Asus or MSi or others, then I'd skip it. If the seller doesn't have a good record of positive feedback, skip it. If the card has problems, like the HDMI doesn't work, skip it.
Just ask yourself "If this business has a card worth around $100 in today's market, how does it make sense for them to sell it for $50?". On the other hand, if they have a card that's worth $20 and they sell it for $50, that makes perfect sense if they want to make a profit. That's why you can't trust deals that look too good to be true.