I had a guy steal a load of my models from my site and post them up on Turbosquid, where he tried to sell them as his own work and make money from them. Fortunately he was no 3D guy and it was quickly noted by some of my friends in the 3D community who recognised the models as my free work and informed me.
When I informed Turbosquid and told them the guy had stolen my work (and 3 other modelers stuff) they hummed and hawed and asked for proofs, etc. When we then also pointed out he was selling our non-profit fan 'interpretations' of copyrighted designs they banned the guy and took them all down right away with no more questions. They dont mind bugging Joe Public, but they dont risk a suit from Lucasfilm, Viacom, etc.
If you pay him to make one or two pictures and you keep it between you guys then fair enough, but dont broadcast it as someone might leap in and call foul. Selling the mesh itself is very dodgy. Any meshes I've made for TV shows I've had to make sure I dont release the model, since the show or FX company that paid me to create it has the copyright.