Best way to test the quality of a scope is to use a broadband LED laser 450nm center wavelength, and use a detector to find the back reflection and the loss thru it both from the ocular end and the objective.Even better is to test it atvarious freq using a thin film optical filter. But even that does not cover the spectrum of light detectable by the human eye.

One thing I do, is when in a store, view something far away but with alot of contrast. One way to achieve this is to find a hole (kinda like a cave) and put something readable inside and try to make it out from 30 yards or so.

Also, all pieces of lenses are not equal. I have found ziess that wasn't as bright and clear as a leupold and viseversa. Ask to see the scope out of box, not demo, and buy that scope you find desirable. You could test Back reflection out of 18 different scope and find one at the top end and one at the bottom end.