Stress marks look like dark circles/lines under your beardies chin, belly and sometimes tail. Sometimes they look like cheeta print. With no stress marks, he should be white/cream underneath with no marks at all.
If you just got him, he will probably have them for a little while until he settles in. If when you take him out and they look darker, you shouldnt bring him out until he gets more settled. You can hand feed him to build trust, that way he associates you with treats instead of as a threat. Make sure you always approach him from the side so he can see you coming, they have a third eye on top of their head that detects shadows as predators because in the wild birds are a big threat. Even if your tank opens at the top, just talk tohim and let him see your hand before you pick him up. And always make sure you support his feet, this will make him feel more safe.
if he is really scared of you, you can just pet him in the cage a few times a day and talk to him in a soft voice. Or even put a peice of clothing that you wore for a day in the tank with him so he gets used to your smell.
Hand feeding will work best though, just make sure he doesnt get used to it too much or youll be hand feeding for a longgg time
Another thing ive learned works really well when you first bring them home is taping paper to the sides of the tank so he can only see out the front. This will make him feel more secure and not worry about him seeing his shadow and getting scared. It worked wonders for my girl when i brought her home.
Good luck, and he will be settled before you know it!!
