If you want a more concrete rule, if you are making about half of your annual income from cosplay-related activities, you would be considered a professional cosplayer. Most people wouldn’t call themselves professional cosplayers until they are making a substantial percentage of their annual income from sponsorships, appearances, or modeling opportunities that are related to the hobby. This is what many people immediately think of as professional cosplayers, but only those that make it to the top tier end up getting invited to conventions as guests.
