Well, here's a start, and it's a pretty big anime convention:
"Masquerade Costume Rules
1. This event is for amateur costumers. Professional or compensated seamstresses, tailors, costumers, clothiers, performers, etc. may not participate in competition."
And yes, Sarcasm-hime is right. I suppose what I meant was that professionals were allowed to compete in master categories, or at least have stage time. Sorry to generalize.
Danzikumaru: I understand what you mean.
Of course, anime conventions are just babies compared to the older sci-fi conventions. My point was that anime conventions are growing, and I find it discouraging to serious cosplayers to create a ceiling for competition. I don't expect a full-blown masters category at every convention down to small cons with 500 attendees. That would be pointless. But for larger conventions, especially ones like expo, that are leaders in the con community to begin putting up walls like this; well, I find it disheartening for the future of anime cons. Hopefully it will change.