The party which decides to show the advertisment in exchange for payment, should be more responsible for what they are showing than a free user posting content.
Now things become interesting when a users pays for ranking or 'verification' checkmarks. What makes that content different than a paid advertisment?
Speaking of responsibility: I want ad networks (a scourge on modern society) to be very liable when their systems are spreading malware and scams.
IIRC the last time my mom came to me with a fake "You Must Upgrade Now" ad on her phone (from an otherwise-legit puzzle game), the ad-network did have a feedback function... but strangely there wasn't any category for fraud.
It might be less of an issue if there were clearer ad-vs-not boundaries, but that starts getting into issues like the browser security line of death [0].
I came to the comments to express the same sentiment, expecting to be an unpopular opinion. Pleasantly surprised to find your comment at the top.
Hosts should make sure they know who is posting content on their platforms, so that in the event they are sued, they can countersue the creator of the content.
Anonymity should not be possible if you pay/receive money for it. Anonymity should be possible if it doesn't involve money / contracts with money. See my sibling post on my view.
Now things become interesting when a users pays for ranking or 'verification' checkmarks. What makes that content different than a paid advertisment?