When a person or company sells items through Amazon, they receive a special ID that uniquely identifies them on the Amazon marketplace. You can decipher this vendor ID from the URL of the vendor's main storefront page. When you need to deal with issues with sellers, you can use this vendor ID to help you in your communications with Amazon's customer service department.
Visit Amazon.com and click on the name of the person or store you want to get the ID for so that you visit their storefront.
Highlight the URL of the main storefront page and look at the end of the URL for a section that looks like "&seller=."
Copy and paste the series of numbers and letters that follow "&seller=", as this is the vendor ID of the particular vendor that you are looking at.