Learn about your scope. Even the high priced ones can show some problems that if you are aware of them, you can deal with.
In this test, was a cheap 2-7X Barska.
First test (no pictures):
I set a sheet of small news print out at short range (like 15-20 yards), adjust the scope to the best it can give, and take a critical look at just how much of the fine print it can resolve. Pay attention to the edges of the field of view and how straight and evenly spaced the lines seem to be. There are special printable targets for this kind of thing, but a sheet of the paper's classified section works just fine.
Blurred edges that can't be read when the center if readable.
Lines that seem to bow or curve.
Second test (variable scopes).
Sight in. Set up one target. Shoot 3 shots at each power. In my case, shot 3 shots at 7X, 3 shots at 6X, etc, for a total of 18 shots. Have to admit, after using the scope at 7X, 2X looks like things shrunk...lot harder to hold center at 2X than at &X.
REJECT: any scope that shows a sever change in POI with a change in power.
Third test: Squaring the scope.
With the scope sighted in, add a number of clicks elevation, sight on the same target, and shoot a group. Add the same number of clicks windage and shoot another group. Add the same number of DOWN and shoot another group....and then the same number of reversed windage. You end up with 10 shots on the starting point, and 5 shots at each of the other 3 corners.
1.End up with a square.
2.End up with back where you started.
REJECT the ones that don't do the two above things.
Figuring 35 clicks and 20yard range, this scope works out to very close to 1/6th MOA clicks rather than the 1/8th advertised. Really not a big issue, so long as you are aware of the real value of the clicks (and this is why you test).
Believe the elevation adjustment is gives slightly larger click values than the windage.
Cheap scope, but it has held its point of aim well over a few years, has reasonably good repeating adjustments.