used scopes rarely bring more than 25% of retail, and Leupold has a lifetime repair warranty, regardless of who owned the scope originally. You can't go wrong with a used Leupold, at 15-20% of retail-cost. Ideally, find one that's fogged, missing the crosshair, for 5% of retail, and get it fixed.
I never seem to run across deals like that on used stuff. Most of the used stuff I see at gun shows seems grossly overpriced to me. I also seem to have this mental disorder of wanting the latest and greatest which is always expensive.
I have a lot of friends who shoot benchrest that rave about Nightforce scopes. I don't think I ever actually looked through one though (afraid I might like it too much - but it's not like I could afford a US Optics scope either). Leupold Vari-X IIIs seem to be the upper limit of what I can ever afford.
gunshows(dealers) are not the place for deals, with the possible exception of late on Sunday, with guys from out of town. The guys to buy from are the ones who are walking around with something to sell, like you are. If they want $250 for the rifle and scope, and you offer them $70 for the scope, they will often enough strip it right off of the rifle,on the spot. Bring your own set of screwdrivers and allen keys.
Every once in a while I would find a deal on Ebay, but honestly I haven't been there for a while. I have picked up several Leupold 6.5x20 Var-X IIIs for around $385 in the past.
Ebay has become more of a sellers market then a buyers market, though, so bargains aren't as easy to come by as they used to be. But if you are on your toes and watch for a "buy it now" price when it first shows up, you can sometimes do OK.
Heck too many people use automated bidding programs on Ebay now. They can be programmed to place the bid in the last 20 seconds (or less) of the auction. I've watched auctions that would get 30 bids in the last 5 seconds. No way in hell you can beat that doing it manually.
That's what I really only look at the "Buy it NOW" auctions any more.