Nickie: You absolutely did the right thing. As Katherine says below, the artist was unprofessional.
I know it was probably difficult for you to confront him, but rest assured that you are correct in this instance. He needs to be taught how to behave more professionally.
In the future, definitely get a contract with these provisions in it. Sit down and discuss what you expect from your artists.
And I would truly reconsider the 10% thing. With all of the work you do, you deserve more than that.