Is it used, that sounds like a decent deal. But I don't see the point in spending 600 on a graphics card. Even 300-400 is quiet a bit of money. You should be good for 3 monitors at 1080p.
I would probably sell it, but selling cards is tough in my opinion. You wouldn't get as much as retail for sure. Still probably make good decent money on it.
I have 2 gtx 470's I can sell so the card only costs $300