Well i see many people giving you know some a 10 to 8 on a level 5 tree.
Really its on the viewers eye. but i once read a brief description on how to judge in a bonsia book . I dont remember the name. But it said something like this you should start by looking from the bottom to the top. First the roots then the trunk witch should be in proportion with the roots. Then the foliage or pads. And finally relations with the tee and pot.