How long have you had him? Young chams can get little black marks on them from from being caged with their siblings.. Bruises, scratches & bites show up on chams skin as black marks. These will usually go away.
A wild caught cham would have black marks because of the dangers of living outdoors that all wild animals face...and also rough handling while being caught and while in transit.
WC is wild caught. Unless he is a WC from Florida he is CB, captive bred. Was he housed in the cage with other animals? If not it could be from before the pet shop got him. The marks look as if he was housed in with other animals and they climbed on him. They should disappear in a few sheds. Other than that he looks pretty healthy and nice!