Block lists
Publishers have the option to block advertisers from appearing on their websites. They use whatever reason they wish. Many have had a ball blocking ads. Reasons to block incude ads which are low-paying, slightly off-target, or competitive. The problem with being filter-happy is you may inadvertently blocking the best targeted, or best paying, ads from appearing.Blocking ads of competitors or companies whose ethics are disagreeable, is the best reason. This is what it was intended to do.
The problem with filtering is because it's not ad-specific. Theoretically, you are blocking hundreds of other ads associated with that advertiser's URL. These ads could be completely relevant, and pay well!
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Advertisers aren't just running the single ad you just blocked. Many run hundreds, or thousands, of unique ads. While you believe you are blocking a single irrelevant ad from appearing, it actually goes well beyond that. You may be blocking thousands of other ads. These could be completely targeted and relevant to your site, and top paying!
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