Here's a link from the BigCrumbs site about tax info, etc:
https://www.bigcrumbs.com/crumbs/editW9Info.do
I only skimmed it but it looks like you'd be safe if you earned under $600 a year. I shop constantly and in a year I've only earned about $250. If the link doesn't work for some reason, register anyway to get the information. You don't HAVE to ever use it
Forgot to add...BC has a very helpful community forum and great customer service, much like Auctiva
If you need questions answered there, those folks are very friendly and knowledgeable.