Amazon is not a good example of contextual ads, though. It doesn't generalize:
1. You can easily argue that these "context sensitive" ads are actually personalized ads: They're personalized based on the search query you just made! Amazon context ads are the same as Google/Apple App Store "context ads". Suppliers are paying for higher ranking.
2. It's a shopping website! Of course those context ads are going to have high ROI because they're showing an ad relevant to the thing you're shopping for!
When people talk about context ads, they mean "Why doesn't Facebook or the local newspaper use context ads?" They don't mean "Why doesn't Target put up a coupon for beans in the beans aisle?"
1. You can easily argue that these "context sensitive" ads are actually personalized ads: They're personalized based on the search query you just made! Amazon context ads are the same as Google/Apple App Store "context ads". Suppliers are paying for higher ranking.
2. It's a shopping website! Of course those context ads are going to have high ROI because they're showing an ad relevant to the thing you're shopping for!
When people talk about context ads, they mean "Why doesn't Facebook or the local newspaper use context ads?" They don't mean "Why doesn't Target put up a coupon for beans in the beans aisle?"