As an advertiser trying to get customers/leads to sell a product, I notice that Google optimizes my CPC by slowly "slipping" to lower-class targets. This makes my campaigns cheaper but less productive, as my product is not intended for low-income customers.
More precisely, I can geolocalize people visiting my website. I check visitors location using IP geolocalization. I see that initially visitors come from area like Manhattan and later they come from Queens/Brooklyn/Bronx/NewJersey. I also check visitors platform and I see increasing proportion of people using old operating systems (Windows XP/Vista), also a sign of lower-revenue I guess. Simultaneously I see CPC dropping.
I would rather keep a higher CPC but stick with mid to high revenue targets. I guess many products are intended for target from a certain income level, so this is an issue for many marketers, right?