Since PPC stands for Pay Per Click, I'm think you should be charged for the click and not the delivery. If it were called PPD, then you should not be charged. While many experts have expressed their opinion, I would be concerned about using PPC until the company you work with give you the exact answer.

If the ad company was successful to get someone to click on the add, they should not be penalized if some people that click on adds have added Hosts.txt. I doubt if people that add the hosts.txt go around clicking on ads.

Donson
"Your Janitorial and Office Supplies Store"