Trial versions, or limited versions, are allowed, provided the Pro version of the code is GPL compatible. Basically anything that sits on your WP install Must be GPL-cool :)
They are showing off their website addresses on final output and giving no way to change it as not providing source code.
Having a non-opt-in link on the front facing part of your site isn't allowed (except in rare cases where the code putting in that link is from code running on their servers, like YouTube branding). Basically the code that's in the repo needs to have all links opt-in. There is, of course, more to it than that, it's sort of like the API thing. If you have a legit reason, it might be okay. If you're spamming, or scamming, it's not.
Are you saying that the code, when in use on your site in a post, has a link to their site? If so, please email plugins AT WordPress.org with the plugin URL and that information :)