Have you installed and tested the card? Doing so will do two things for you:
1) You can use Device Manager and other tools to help identify the card.
2) You can determine if the card actually works or not. If not then the card should be properly recycled.
Overall the first question any potential buyer will ask is "does the card work"? You must be honest about your answer.
Other things you can do:
Take a close look at everything printed on the board. Google accordingly.
Keep in mind that the card could be a counterfeit card and the search results may not be helpful. You can search GPU images and compare your card to those images. Look for components and their respective placement on the cards. Genuine cards will simply look (subjective) better. Bad soldering, bent components, flimsy, structure could be indications of a counterfeit card. Poor quality to sum that all up.
To post an image:
http://www.tomshardware.com/answers/id-2173703/post-images-tomshardware-guide.html
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