we've got to make sure that no one's direct linking to the artists gallery, unless they've got consent to do so...that proves to be a big problem ^^;
and also make sure to say something about how even though they've marked a "deadline" that the art may not be finished and they can't really do anything about it because they've put nothing into it other than a request.
....As for something major....not everyone wants just avatar art..but Original Character art as well, meaning they would have to provide pictures they've already had done, concept sketches, the infamous 'he looks like a mix of this and this' or at least a detailed written description. Original characters also tend to take more time than avatar art because the artist has nothing fixed to base it on...usually.