Let's say someone takes a free WordPress plugin from https://wordpress.org/plugins/ , improves it and then sells copies of it for money.
It appears this is possible, BUT then the buyers of that paid plugin could probably distribute it as they see fit.
From what I understand, if a premium (paid) WordPress plugin uses entire sections of a free open-source WordPress plugin, then that *entire* plugin is supposed to be distributed under the same GPL license.
In practice though, WordPress doesn't really seem to enforce this, because they *want* more marketers creating plugins and helping spread the word about WordPress.
Not too sure if the original developers of the free open-source plugin would be too happy about that though.
And what if the premium plugin developer adds a licensing function that stops someone from using the plugin without paying the seller of the premium plugin?
What do you think?