I've been looking at the artist gallery, it's clear that they don't have a defined style yet, their work kinda seems like traced from some photos/3D models...To be honest I don't know how the client expected something stylish with their oc by looking at the artist gallery tho :S also for something that probably costed like $10 usd. I'm not defending the artist, how they acted still was very unprofessional and I hope they learn and improve with the time, offering wips to avoid that kind of problem and let the client to ask for corrections, but the client was very disrespectful too, they could have been more soft when asking for changes and offered better and detailed feedback to make the artist understand. My advice for the client would be, if you want decent art of your character, choose an artist that shows a nice artstyle in their gallery, an style and skills you really like, and it probably won't very so cheap.