In that case it's just in the hands of individual publishers, so results will vary. Plus publishers will make more money if they _don't_ do the right thing and police out the bad ads (at least in the short term).
Traditionally, publishers didn’t mind publishing ads for scams like sea monkeys or x-ray specs, but they found it embarrassing and put them in the back of the book in small print. The bizarre part of the internet is that the scams go on the homepages of sites.
> "Never allow dynamic ad content! Ads should be individually approved by publishers and not subject to change after approval."