What you must know--a tax permit--sometimes called a resale certificate--is required by your state of residence if you are going to be reporting sales tax to your state treasury. If you are selling physical products on eBay or any other selling environment to residents of your state, then you will have to report your income and pay sales tax. If that is the case, then you will need a sales tax permit.

You must also know that you will need a sales tax permit in order to purchase products from true wholesale businesses. Your sales tax permit grants you the legal right to purchase wholesale goods without paying sales tax. You, in turn, as a retailer (online or off) must charge sales tax to any residents of your state purchasing from you. A true wholesaler, by the way, is required by law to have proof of your sales tax permit in order to sell to you. In the United States, if a business does not require proof of your tax permit, it is not a true wholesale business.

You can get a sales tax permit from your state department of revenue. Tax permits are usually free and obtaining one is generally no more complicated than filling out a simple application, something that can often be done on the Internet.

I want to add that there is no specific license or permit specifically for drop shipping products from eBay or any other selling environment, online or off. For most eBay sellers, single person businesses and sole proprietorships, this will be the only permit needed. It is not generally the case that you need an EIN (Employer Identification Number) unless you pay wages or incorporate.