The best way to tell is to turn the carb upside down and wiggle the throttle lever up and down(not side to side)but do not move the throttle open.
You are looking for any wobble or movement of the butterfly(s). Also be sure that the other end of the primary shaft does not allow the butterfly to move or wobble.

The 2nd way is to actually try the carb out on an engine and see if there is an erratic or inconsistent idle or a whistle, David.