I had this problem about a week ago, where someone had ordered a model in stainless that was too thin for stainless. In the model restrictions area, if you want all but stainless to be acceptable you have to keep clicking add until all that is left is stainless. What about a remove material button? That way I can go on the list and just say no to stainless? What about instead of the way it is now, have check boxes with a check/uncheck all button? Then you could simply uncheck stainless for none stainless models, and for stainless only click check/uncheck all and then click stainless.