As an artist, can I post the art I make for people?

[theatomicace]

Obviously the art I make for them is theirs to do what they want with, I feel like that’s a given. But as the person who drew it, would it still be acceptable for me to, say, post the art on my Instagram with a watermark and say that it was for a commission? I just don’t want to deal with any hassles if I were to do that and it ended up not being allowed.