Don't buy used optics that you haven't examined. Many owners leave rifles with scopes on them or their binoculars in a hot car and the lenses and prisms fog from vaporized seals and maybe glue. The result is a cloudy view. If you buy used optics sight unseen and they're okay, you were lucky!
I once bought a used Zeiss 8X30B monocular that I eventually realized was fogged a little that way, before I learned much about optics. I sent it to Zeiss USA and they cleaned it as best they could, got maybe 85% of the residue off. Said that more was impossible.
Take a flashlight and shine it into the lenses and look around inside the instrument. Is there any fogging? Debris from manufacturing that should have been cleaned off? Fingerprints? The top Euro makers are much more likely to deliver pristine wares than those in the Orient. Some Oriental-made ones are excellent, but quality control seems to vary more than for Zeiss, Leica, or Swarovski. I say this after reviewing a number of binoculars when I wrote professionally, and I examined others at the SHOT show. I was also a guest at a Zeiss seminar that lasted several days, including the opportunity to try their and competitive brands during both daylight and at night, at a remote location where light pollution was minimal. A scientist came over from the factory and taught a course to the invited writers as well as to train their own managers. It was a wonderful experience, and very informative. I also have several books on optical goods, esp. on binoculars.
If I was looking for a new scope and couldn't afford Zeiss or Swarovski (both of which are astounding compared to most lesser 'scopes), I'd try to buy a Leupold Vari-X III in 2.5-8X. For a hunting rifle, that's all you need and the quality and service are excellent. It suits most calibers for all but specialty long range varmint rifles, where you'll want more power on a heavy specialized rifle.
I hope that Leupold still makes that 'scope. I haven't checked in years.
My son's favorite Winchester M-70 Fwt. Classic .30/06 wears a Zeiss 3X-9X, and it is all he needs for most that he'll ever encounter. He sent some photos of targets that he shot off the bench with that rifle, and they are as good as a light hunting rifle is likely to shoot. I think he showed a quarter (25 cent coin) by the holes and it'd have covered all five shots. He said that the clarity and sharpness of that Zeiss 'scope helped to do that.
Many choose 'scopes that are too powerful for fast use on game at average ranges. I leave the 'scopes on my rifles set on 2X-3X unless it's apparent that shots will need to be taken at extended yardage. VERY FEW men should ever fire at living animals beyond the range at which an 8x or 9X scope allows a good view of the target. I used to work as a range officer, and I saw many sight-in rifles and practice before hunting.
Most were not too familiar with their rifles and didn't handle them instinctively, nor did they shoot especially well, although the available range was just 100 yards. The idea of these guys popping off at deer, elk, or pronghorn at 400 yards or more is not a pleasant thought.
Modern 'scopes are quite a bit brighter and sharper than the old ones. And the selection of reticles is better. I like the German one with three heavy crosshairs and the top one thinner. But what Leupold calls the Duplex is probably most popular, and it likely should be.
I hope this helps someone who might need the info. BTW, I am not now nor have I ever been employed by any optical manufacturer. I just call 'em as I see 'em. But I am an enthusiast of fine 'scopes and binoculars. They give great joy in life.
