No, that's why I said 'unsolicited' rather than 'third-party', so take the motorway billboard toll road example - if you also happen to own the car dealership or the webapp, you can't advertise that, because that's not what I've come to your motorway for.
And what's solicited or 'relevant' doesn't need to be rigidly defined in statutes (assuming common law) - the ASA or OfCom whoever it would be (UK examples) slaps fines on the rulebreakers and if they think they've interpreted the law correctly in good faith then it goes to court and we find out (and the growing body of case law helps future would-be-advertisers interpret it).
The existing advertisement disclosure rules for social media for example don't allow the loophole you propose: a 'sponsored' segment shilling a product in a YouTube video isn't considered different from directly selling video time to the third-party in which to run their own ad reel.
And what's solicited or 'relevant' doesn't need to be rigidly defined in statutes (assuming common law) - the ASA or OfCom whoever it would be (UK examples) slaps fines on the rulebreakers and if they think they've interpreted the law correctly in good faith then it goes to court and we find out (and the growing body of case law helps future would-be-advertisers interpret it).
The existing advertisement disclosure rules for social media for example don't allow the loophole you propose: a 'sponsored' segment shilling a product in a YouTube video isn't considered different from directly selling video time to the third-party in which to run their own ad reel.