That's not really true. Advertisers can bid on how much they want to pay for each individual impression. Advertisers will likely bid more for ads on high quality websites. Advertisers will also bid more for people willing to buy stuff.
Citation needed
> Advertisers will also bid more for people willing to buy stuff.
Unfortunately, there is no correlation between people willing to buy stuff and high quality content.
> Unfortunately, there is no correlation between people willing to buy stuff and high quality content.
Citation needed :)
Seriously, the "enlargement penis" spam works because the average person is not that selective on the ads they chose nor the websites they visit.
I don't think you understand "average". It's the extreme tail of the distribution that is targeted by such ads.
Example:
> Nigerian scam emails 'deliberately implausible'
> New research from Microsoft suggests that email scammers maximise profits by entrapping only the most gullible.
http://www.telegraph.co.uk/technology/microsoft/9346371/Nige...