well quality is in the-
hardware- does it look more than adequate for the model. for example did the manufacture give you plastic horns on a 1.20 sized plane!
glue- if you look, dis they use a glue gun? are most if not all joints glued.
wood- do pieces look warped does it have a lot of grain or is it not smooth because of the grain
covering- does it peel easily, does it have wrinkles...etc

The best manufactures are mainly from towerhobbies, h9, wh, dp, qq, ef and chief. If you buy and arf, most of the time if not all you will find that you could rate it anwhere from an 8-10 out of 10. most of the time it will just be bad hardware!