I just found out something very interesting and useful about AdSense, might not be totally legal though.
This trick allows you to increase your eCPM. As you all know, there is a "publisher id" that Google AdSense provides you. As some of you might have experienced before, once you delete the publisher id, the ads will keep being shown on the site, but you will be publishing them for no cost by Google's side. So you will be publishing freely. I will tell you something that won't bother you to leave your AdSense code without a publisher id for 4-5 days.
I did a test about this, and the result was great. I removed the publisher id. The first 2-3 days, AdSense spider almost never left my site (the same site we're talking about here, before with publisher id, and after without publisher id). The following 9 days, the spider never came to the site though. But guess what this test taught me? After I removed my publisher id for 2-3 days, when I put my publisher code again my eCPM was as high as $1,2. I was getting $1,2 per click and the ads shown were high paying ones instead of those crappy ones. That was an amazing experience for me.
As a result, once your earnings start to decrease, remove your publisher id for a few days, and put it back later again. Or you can just do this periodically to keep your eCPM high. You will earn more than you lose for sure!
PS. The site I used in this test was about "women" and had been considered as trash before I made this research. The test had been applied on 2 different accounts, and both tests were positive.