What I do with any new to me binocular is to examine how closely the barrels are to each other optically. Do you get the same degree of apparent sharpness with both eyes, or is one side either noticeably strong or weak? Does the diopter focus the eye with minimal adjustment or do you need to do a bit of fidgeting to get it right? Does the diopter stay adjusted from one day to the next or do you have to reset it every time you use it? Focus on a power line or roof top, something with a long straight line and move the binocular away from your eyes. Does the power line stay as one line, or it is higher on one barrel than the other? Does the binocular focus with minimum fuss or do you have to roll back and forth over the object a time or two to get it focused.
There is more, but if the barrels don't focus equally, if the line splits, or if the diopter is funky, or the focus is not right, then chances are you don't need to look for much more.
If it passes those basic tests, start looking for build issues, fit and feel and other image parameters.
The most important view you will ever get from any binocular is the first one, so pay attention.
