You don't need a company structure to sell on Ebay. You would just claim any of the revenue/income/expenses on your personal federal tax return. Google 'how to tax self employed' and you'll find some good articles.

If you sell alot in your own state, however, there may be some sales tax that apply. You would need to call the local state's tax office for that info.

When you are talking about an e-commerce business you’ll not only have to pay attention to the needed business entity, but also to a few more factors.

Business Entity. An e-commerce is not different from any other kind of business. You can choose from structures like LLC, S or C Corporation for sole proprietorship, partnership and limited liability companies.

Choose structures that give your business a separate legal and tax identity from yourself. Yet, many businesses start as a sole proprietorship and when certain level is reached, they change their structure.

The second important things are investors and VCs. If you’re interested in receiving capital from third parties, they will probably become more interested in the business if it is a C Corporation. The IRS website has plenty of information about LLC, S and C Corporations.

The second factor you should look for e-commerce purposes is Sales Tax, which has adopted some type of formal position for online sales. I suggest asking to your state tax agency for further information about this point.

Finally, I’d like to mention Trademarks and Domain names as important factors for e-commerce. Your domain name is a very important element of your website, so when thinking about how to protect it, trademarks are probably the best option. A trademark it’s a symbol or word used to identify the source of goods to consumers. Trademarks are complex. Here you can learn more about them.