mostly i just look at it- is the edge fairly straight with no platform remnants? Is the tip especially sharp and thin? is the transition to the wrappings and shaft smooth? Is it hafted straight?
Also, i usually test the tip by LIGHTLY pressing it into my lip- this is probably not nececary, haha.
If you are hunting with the stone heads you bought, you may want to get an experienced knapper to sharpen them- most people do not make them hunting sharp if they are for sale (unless sold for hunting), and most heads get dull as they bump up against other points, or anything , really.