Some flea markets / farmers markets will require a sales tax number to do business. If the flea market or farmers market you are dealing with does not require a sales tax number, you still might need a business license.
Click on the states below to get information on obtaining a sales or tax number. Some of the states allow you to apply online and others will give you forms to download, fill out and mail in.
Some flea markets/farmers markets will even help you in the process. Contact the flea market you want to set up shop with and ask them what the requirements are.
District of Columbia