Not professional

Got very helpful response from XRX. They understand that it's a fuzzy definition and people can be confused. And they drew what is, in my opinion, a very clear and reasonable line:

A simple rule (that we think is fair) is that if you haven’t made more than $500 (a prize amount for aspecific amateur category in the Think Outside The SOX contest) then you are still an amateur. If you teach the occasional class here and there, you may or may not be considered an amateur – but that would really depend on how much you teach and how much money you've made from teaching. In most cases, we find that knitting and crochet instructors – paid to teach others – really are professionals; at least in the eyes of their students. Again… we try to use the $500 rule here as well.

I haven't made anywhere near $500. So I'm free to enter as an amateur.

Soon you will all tremble before the awesome spectacle of my evil sock designs.