F1 student and eBay selling tax
If you have income - it should appear on your tax return. If you are a non-resident, that would be 1040NR, with the eBay income appearing on line 21. Since this is unrelated to your studies, this income will not be covered by the tax treaties for most countries, and you'll pay full taxes on it. Keep in mind that the IRS may decide that you're actually having a business, in which case you'll be required to attach Schedule C to your tax return and maybe pay additional taxes (mainly self-employment). Also, the USCIS may decide that you're actually having a business, regardless of how the IRS sees it, in which case you may have issues with your green card. For low income from occasional sales, you shouldn't have any issues. But if it is something systematic that you spend significant time on and earn significant amounts of money - you may get into trouble. What's "systematic" and how much is "significant" is up to a lawyer to tell you.