I have been showing my quail for a few years and in actual APA shows you usually won`t be abllowed to enter quail since they are not in the standard of perfection. But in events where you can show them like local fairs and 4-H events this is what judges will look for:
1. They will judge on how round the body is, and how round the head is (For coturnix, the bigger the better)
2.They will mark you hard on condition, make sure your birds are cleaned well before the fairs. If its missing feathers or dirty you will lose marks!
3. Colour pattern. They will use similaire judging to poultry. So if its a White Coturnix, then it should be all white! So make sure its got proper colouring because they will know!
This is what i have learned from talking to various judges from all over Canada and the United States. Not all judges are the same but this is what the majority of judges will judge them on.
If the judge has raised quail then he will judge them on what i just said and maybe more.