I think, if this happens, it will be quite a large sum of money before they start looking at it for tax purposes. Seems to me I read recently that if you receive more than $30,000 (? could have that number wrong) as an Amazon vendor or half.com/eBay vendor that it will be reported to the IRS as income. They are probably trying to arrange something similar with PayPal.
Edit: Okay, I found a link similar to what I was remembering. Here it is:
http://www.weberbooks.com/selling/20...-purposes.html