Sibling commenter identified an alternative as to charge for (presumably a proportion of) ads in a timeframe. That seems to satisfactorily mitigate almost everything:
1. Clicks are not charged for, so increasing clicks does not change the cost.
2. The only question available is how much you pay and how much you make. Page owner's rival could attempt to confuse you but there's not actually a difference between paying $1000 for 0.1% of ads shown in July, getting 100 clicks out of 10000 impressions and making $2000 vs paying $1000 for 0.1% of ads shown in July, getting 10000 clicks out of 19900 impressions and making $2000.
3. Shorter 2: Numbers are irrelevant unless they have a dollars/euro/yen/pound sign before them.
4. Clicks to not come out of the advertisers budget.
5. Surveillance advertising enables this fraud by attempting to distinguish between real and fake traffic. If you are paying for something that is robust to that, then the fraud is irrelevant. In particular, it doesn't matter if 0.1% of ads displayed to bots are yours and 0.1% of ads displayed to humans are yours if you've paid for 0.1% of ads to be displayed to be yours using a random rotation.
The only thing like any of these hacks that seems relevant is that a very crafty adversary might be able to determine your traffic rate and identify the timeframe they need to request to particularly target a certain ad, making more of the 0.1% of displays get shown to a bot. But this is easily handled by using a secure random rotation rather than say a round robin rotation. In any case, I can independently verify the efficiency of my spend by getting a sim card that the ad network doesn't know about and repeatedly reloading the page for a month. If I receive only 0.01% of displays because some third party or the network is trying to defraud me I now have pure evidence that they aren't upholding their side of the deal. If they try to verify humanity before deciding what to do, then they can just say "no, we identified these requests as coming from a bot and graciously didn't display your ad to them". What can you do? The existence of surveillance is not in the interest of the advertiser who is concerned about fraud.
(If you don't trust your network, any fraud on their part isn't going to get solved of course. But then having less data is an advantage. There will be fewer variables so it will be easier to catch, and the capital requirements will be simpler --- code and business partners vs code, business partners and user surveillance data --- so it will be easier for a trustworthy competitor to emerge.)
1. Page owner / Ad network / Ad space auction market middleman fakes clicks to get click revenue
2. Page owner's rival fakes clicks to devalue ad spots
3. Advertiser's agency fakes clicks to make numbers go up
4. Advertiser's rivals fake clicks, to waste advertiser's budget
5. Ad networks 'accidentally' classifying legitimate clicks as fraud, to reduce payouts to page owners.