You're underestimating the general underhandedness of people. If I can sell all my website's ads once, why not try to sell them twice? Double my income. If Sam

You're underestimating the general underhandedness of people. If I can sell all my website's ads once, why not try to sell them twice? Double my income. If Samsung's marketing people are in Korea, I'll show all Asian IP addresses their ad, and then show some other ad (or ads) to the rest of the world. Of course, Samsung may notice the low volume, so a better scheme is to also load their ad elsewhere, but placed on the page so it's not visible. If you look at the Javascript that gets served with the ads, there is generally a hunk of logic that tries to confirm the ad is genuinely visible, to try to deal with that last bit.