Highly experienced aro farmers and hobbyist can distinguish adult aros' sex by head and body shape. I can only guess more accurately when they start pairing. Usually the aggresive and croacking one is the male.But the only 100% way to be sure is when you see the female drop the egg.
For one main reason why Aros cost so much is the fact that identifying sex of aro is next to impossible and or 1 in a lot!.....there's thoughts and method as per the above, but very very difficult since most buy them so young and unless you have lots of aros that you have raised from import size in Canada to choose from....pairing is difficult.