In most states, you need a permit from the state authorizing you to sell goods to, and collect sales tax from, customers within the state. As the seller, you are responsible for charging sales tax on purchases made from your eBay store or via an eBay auction if the goods ship to a location within your state. For more, review the section on Paying Your Taxes. In some states, the seller's permit also allows a seller to buy items from wholesalers (for resale to customers) without paying sales tax. This is a real money-saver if you are a seller who buys wholesale lots from jobbers or liquidation sales within your state that you plan to resell on eBay. Some states call this a seller’s permit; others call it a resale permit or something similar. (Note: You might need a permit even if your state doesn’t have a sales tax. Even in the handful of states that don’t impose a sales tax — Alaska, Delaware, Montana, New Hampshire, and Oregon — local governments sometimes impose sales taxes, which you may be required to collect and submit to the appropriate agency.)
If your state requires a seller's permit, don’t make sales unless and until you get one. Getting caught doing business without a permit will likely result in you having to pay the sales tax you should have collected from your customers, along with a fine.
Finding the forms. You can find information (and in some cases, forms) on seller’s permit requirements at your state tax agency’s website. To find a link to that website, check the list provided on the Small Business Administration website, at the Multistate Tax Commission website, or among the state links at the IRS website.