Some countries have property taxes where you declare the value and the government retains the right to purchase the property for that value for example.
My first thought was to make the advertising cost driven by revenue on the site. But that just reverses the incentive.
Altering data would mess with everything. Why is unverified traffic increasing? What's wrong with new marketing efforts? Marketing just requires fixed definitions. e.g. if you have 97% bots but it remains constant that's okay. I know I am spending $x to get $y conversions. I can plan over time, increase or decrease and I can plan. I won't be willing to pay as much as with 0% bots (will pay far far less) but I can set my strategy on this.
It's not that it's x% bots that is the problem. Growth team doesn't adjust strategy on percentage-bot. Growth team adjusts strategy based on return on ad spend. If 0% bots but no return, way worse than 5x ROAS with 99% bots.
In others you'd want, say, auditing or independent third-party verification.
In this case, perhaps an audit involving the deliberate injection of a mix of legitimate and bot traffic to see how much of the bot traffic was accurately detected by the ad platform. Rates on total traffic could be adjusted accordingly.
This of course leads to more complications, including detection of trial interactions, see e.g., the 2010 VW diesel emissions scandal: <https://en.wikipedia.org/wiki/Volkswagen_emissions_scandal>, or current AIs which can successfully identify when they're being tested.
That's a subset of multi-party decisionmaking situations, though it's a useful one to keep in mind.
Basic ad ops has ad buyers buy ads from different vendors, track which converts (attribution, which has flaws, but generally is decent signal), and allocate spend via return on ad spend. So it hurts the vendor at least as much as the buyer by inflating the cost per action / damaging roas.