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Adsense has an accurate way to detect invalid activity. A site with more than 5,000 page views a day should not get over 3% CTR. Even above 2% is very suspicious. Google knows the average CTR of each market/niche. And if they detect something abnormally high CTR continuously, then they will disable your account for invalid activity. However, for a small site with less than 5,000 page views per day can have a high CTR above 5% once in a while (but not continuously) and that's ok.
[edited by: jbayabas at 6:38 pm (utc) on Sep 8, 2012]
jimbeetle, I based this observation as a publisher for 8 years with high traffic sites.
As we know, all sites are different and it's very difficult to make statements to cover them all.
The highest CTR I received by the end of the day was around 0.75%.
A high traffic site should never have less than 1.5% CTR
they are both completely different AdSense accounts(banking info, names etc.)
Nobody in this forum - nobody - can speak with authority about what is normal or average for any sites other than their own, no matter what they think or want the rest of us to think. Remember that. Only Google has that information.
...they get what they deserve.