There are some niches that are overflowing with stupid advertisers that are bidding higher than the amount the referral is actually worth. In those cases, there really isn't anything you can do. You can wait it out, but there are rubes already lined up to replace the ones that go bankrupt and leave.
That's why you'll find people swearing both cases..."adsense is worthless" vs "adsense is a goldmine". It really depends on the niche.
That's why you'll find people swearing both cases..."adsense is worthless" vs "adsense is a goldmine". It really depends on the niche.