I do not have data to back this up, from my observation, most people do not know what is or is not an advertisement unless it is flashing. Even then, there is a

I do not have data to back this up, from my observation, most people do not know what is or is not an advertisement unless it is flashing. Even then, there is a not-negligible percentage that does not know. People just click to find out what things are, not because they are interested in the message. Perhaps a simple way would be to ensure that user does not come back to the page within x seconds, otherwise you should not pay.