I don’t understand the question. What is not working for you? You can change a product author to any user with a role of author or above. So Author, Editor or Administrator.
Why don’t you use a switch user plugin and switch to the users account when creating the products for them?
I’m unable to change product author from ‘admin’ to a ‘customer’ role. Ideally I wouldn’t want my client needing to temporarily change her clients user role from ‘customer’ to ‘admin’.
I think this is just a case of not understanding roles and capabilities properly.
You cannot change the Author of a product to a Customer because the capabilities of a Customer are well below that of an Author.
Customer capabilities are outlined here:
Customers mostly have read access. They can view and edit their account information and read past and present orders. That is all a Customer should be able to do.
You would not want a customer to be able to edit product details.
An author has many more capabilites outlined here:
As well as read posts (products are just a post type) they can edit and delete posts.
There are plenty of user role editors for WordPress that will allow you to clone the Author role and rename it something else like “Vendor” or “Client”. If you do that, then you’ll be able to change those to a product author.
Hope that helps!