I wouldn't. New, they used to sell for 250-300. 250 would be the max I would personally pay for one. I'm not sure about the specs, but is it Evga? If so, has the seller registered it and can you use it to step up? How about the warranty on the card? The major downside to buying used is do you trust the seller? Most likely, you're going to want to clock it up to GTX speeds and then you might need to RMA it after burning out the card.
Cleeve recommends the X1950XT for that price range if you're willing to go ATI. It should perform slightly better than the X1900XT.