ad sence revenue down

i read in affilite forms now these days ad sence revnue down up to 90% ,why i think some reason for down the revnue

1. many more sites run the ad sence
2. web master creat a page for high priced keywords and get the traffic , but people not interest to buy the particular products
example:
help desk software key word price around $20 , i see many sites run sites with help desk related contents , people come and click on the ads but noy useing the service or buying the products, so advetiser not get any return?
3.as adsence run in lot of sites many site onwer send invalied clicks , so advertiser not get any return.

tommarow i will right more on adsence related to this subject.


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