Its very easy to tell on the veiled chameleon with the spurs,even when they just hatch out from their egg shells,but panther and other species will require more....
Breeders can absolutely make mistake,but the more experience breeders will make less or none,since their breeding years experience along with their knowledge n keen observations are the key to tell their own chameleon baby's genders and all of these will require lots "TIME" spend,the more time u spend to raise ur baby chameleons,the more u will discover,thats why u see lots great chameleon breeders out there ,their price on their baby chameleons are higher then others,thats because they spend so much time in caring their chameleons n their feeder bug cares(10000 to 15000 pin head crickets,dry gutload n wet gutload).....breeding its the easy part,but raising n caring the chameleon then selling them all,thats a TOTAL different story....and these are my own experiences to share.