Publishers who run AdSense should know about this: A service that blocks low-paying contextual ads called AdSense Blacklist. There’s a real problem with AdSense in that a lot of low-quality ads are running with increasing frequency (the built-for-AdSense-only business that bid high, but aren’t necessarily delivering a real service). If you’re interested in serving readers well with AdSense (advertising is, after all, content), then you want to block these sites from your AdSense rails.