I usually try and give them a chance first. I'll ask them to credit bases or explain to them that you're not supposed to upload art that isn't yours. That blew up in my face with this girl.
First thing she did was make an alternate account to back up her story that the art was hers, then she called me a bitch, then she blocked me and started telling people that I was bullying her. She did the same thing to a few others also.
Some people just can't be reasoned with.