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If Google thinks you are a risk to advertisers, you are gone, despite the amount you make as a publisher.
never stop testing
Don't put all your eggs in one basket especially when Google AdSense is holding the basket.
Mine is always think about user intent. Why are people coming to your site in the first place, and why should they click on ads when they're there?
I believe that the profitable phrases are shopping related followed by DIY project phrases.