“Extensions can be included in premium products (themes or plugins) that are sold to users. In that case, you have to keep the credit to metabox.io. Link attribution is required. The credit must be put on a public and visible page. Credit is not required if you include extensions in your products (themes, plugins, websites) for your clients.”
Regarding the statement “The credit must be put on a public and visible page”:
Can you tell me how I can enforce this if I'm selling a premium plugin or theme – with the MB Frontend Submission extension included – that does not change the front-end code in any way?
By definition, if I sell the product to a third party, I simply don't have any control over how or where it is going to be used. There's no way I can access the backend of an unknown site to add a link on a public and visible page.
So, please elaborate on this. I'm trying to understand it, because it doesn't make any sense to me as it is.