I am not an expert on the physics of optical instruments at all. I do know what I "see" through excellent binos and scopes. I have viewed through so many brands and so many models these past 10 or so years it is almost funny. About everything from the cheapest BSA's to the most expensive Ziess'. And about everything in between .... Tasco, Barska, Osprey, Nikon, Simmons, Redfield, Swift, Weaver, Swarovski, Bushnell , Pentax, Vortex, Schmitt Bender. from about $35 to about $2500 MSRP.
I learned long ago that you get what you pay for in optical gear. There are no secrets in how to design and build top notch binos or scopes. Patents, sure. But no real secrets. Top end glass, exotic chemical coatings, super precise construction, nearly perfect QA, etc. You cannot and should not expect these in low dollar gear.
On the other hand, one can afford what one can afford. So look for value. A great garauntee helps, but some of the poorest quality scopes come with a lifetime garauntee. Listen to hunters, not the advertisement hype. Does not take $1000 or more to get yourself a good scope. Value scopes can be had in the $250-$600 range. Below that, my experience says it is iffy at best. Above the $600 range almost assuredly hyou are looking at great performance. And should be for that kind of $$$.