I understand the OP’s frustration, and I think the idea of a ‘kill fee’ is a great one, esp. if you think advertisers are likely to renege on their deal.
But customers are customers! And they will want what they want, regardless of what you offer, regardless of what they say they want, too! Customers can be quite contrarian!
So, just keep your terms of ad sale CLEAR, SIMPLE, and don’t write to multiple pages for any contract (it won’t be read!). And try not to be angry at your customers/advertisers!
I did set out advertising terms on my PCB site that state:
“PurelyCoffeeBeans does not encourage advertisers to engage in buying page rank. PCB suggest instead that advertisers focus advertising for real traffic or real human visitors as the final metric by which a particular ad campaign’s success is judged.”
To offset the requests that you get, I replied to one advertiser, then rewrote my reply as an Advertising Page on my site. That way, I got something out of the deal even if the advertiser didn’t buy! They didn’t!
You can see what I wrote: .com/advert … beans.html (but if you visit, make sure you click on a couple of other real pages!!!!)
K.