Incorrect. My logic is that a second hand card should be cheaper than the same new card. Otherwise buy the new card. It's really simple.
The used card market is strange, especially locally. eBay works well because it auctions find their own price. I generally find good deals are often hard to come by locally as people tend to value their cards relative to what they paid, and someone who paid $170 for a 750 Ti at Bestbuy less than two years ago already thinks they're getting fleeced selling it at $100. Hell, just looking at things that have gone up today, there's a 280X for $170, a 7790 for $60, a 5870 for $69, an unopened 390 for $300, and a 5770 for $75 Granted I'm in a pretty small market, it might be different if you're in New York or something.