In the Opencart Multivendor extension from Purpletree, any user or customer can register as a seller to sell the product. The seller can create products, get product orders, create own store and create a seller blog, etc. In Multivendor seller can register the following ways:
Seller registering using the seller registration link
Customer registers as a seller during customer registration
A customer wants to register a seller after signup
Admin creates seller

Seller registers using the registration page
Go to the Opencart web site home page, you can see the seller login link is shown on the header. Click on the seller login link.
Add description
After clicking on the seller login link, the User reaches the Seller login page. On this page, the seller registration link is present, click on the New Seller link.
Add description
After clicking the "New Seller " link, User reaches other n new seller registration page, here user fills all required details like personal details, Seller Information, and Payment Details.
Personal Details
In personal details, the user fills first name, last name, E-mail, Password, and Telephone. All fields are required in this form.
Add description
Seller Information
In Seller Information, the user fills Store name, Store E-mail, Store phone, Store Address, Store Country, Store shipping and return policy, Store SEO URL and Social links.
Users can upload the store logo and store banner also. Only Store Name is required here.
Add description
Payment Details
In Payment Details, a user fills store bank details, Store TIN and PayPal Button Id for Store payment.
Add description
If admin approval is required for seller registration then the user has to wait for approval from admin, and if admin approval is not required when the user registers as a seller successfully and can start using seller functions.
Customer registers as a seller during customer registration
Go to the Opencart web site home page, click on My Account and select Register.
On register page fill all the personal information, after that select to "Yes" to become a seller, thereafter you will reach to the seller register page.
Enter the store information such as store name, email address, etc.
Add description
Here fill all the required fields. If admin approval is required for seller registration then the user has to wait, and if admin approval is not required when the user registers as a seller successfully.
A customer wants to register a seller after signup
If a user is already a customer and user wants to register as a seller, then the customer logins to his account and reached on the account page.
On account, page Become a seller link shows. Click on Become a seller link, and the user will reach the seller register page. Enter the store information such as store name, email address, etc.
Add description
Here fill all the required fields. If admin approval is required for seller registration then the user has to wait, and if admin approval is not required when the user registers as a seller successfully.
Admin creates a seller
Admin can create a seller by using the customer registration process from the admin side.
Login to admin panel, go to the navigation menu and click on customers option and select customers. After that click on the Add button.
Add description
Fill all the personal information, after that select to "Yes" to become a seller and fill Seller store name and click on the save button then the seller is created successfully.
Add description
So, a seller can be registered in all these possible manners.
More details of the Purpletree Opencart Multivendor marketplace can be found here. https://www.purpletreesoftware.com/multi-vendor-marketplace-opencart.html