Programmatically creating users and vendors (API, CLI, database inserts, batch)

Hi, how does people create users and vendors from the command line? Does an automation extension exist, for example? Is it possible to insert directly into the database? Does it exist a Command Line Interface (CLI)?

You could use SQL "INSERT into Customer ..." statements, however, there are two concerns:
1) You need to also insert into the table [Customer_CustomerRole_Mapping].  (e.g. the Registered role)
2) If you want to insert a Passwords (into the table [CustomerPassword]), you will need to deal with generating its hash.

Thank you, I will try that. Or, maybe I will let them register themselves first. By the way, is it possible to let everyone have the vendor role, by default?

Not out of the box.  It would need to be done programmatically (old example), or could also be done with SQL.  In either case, you also need to create a Vendor, and set the Customer's VendorId.