http://money.usnews.com/money/blogs/my-money/2012/04/10/what-online-resellers-need-to-know-about-the-1099-kBeginning with the 2011 tax year, IRS regulations require that U.S. payment processors, including Amazon and eBay, file a Form 1099-K for sellers who exceed $20,000 in gross sales and/or 200 transactions in a calendar year. These regulations also require that all sellers have taxpayer identification information on file, regardless of sales volume.
So if you anticipate completing more than 200 transactions, or more than $20,000 in gross sales, be prepared to file your small business income and pay taxes. Otherwise, you will be hearing from the IRS.