I'm looking to enter some cakes into a few contests. The rules state it is clearly "amateurs" only. What makes someone an amateur? or better yet a professional? (BTW, there are no rules or requirements posted that define "amateur".)

Formal training? (including a Wilton class or 3?)
Is it the amount of time you have spent decorating?
Charging for cakes?
Do you need a storefront?
Does it need to be your primary source of income?

If you earn money decorating/selling cakes, you are a "professional" in most definitions.

I thought this would make for some good conversation

I would think that if you have a regular following that buy your cakes and make up a large portion of your income, you would be a pro.

Our State fair defines a professional as someone who teaches classes, or who has taught classes in the past, and who sells their baked goods. (they don't define if this is full time or part time)