Do you agree adsense doesn't work for some marketing niches? I do mean when adsense just pays a few cents per a click. For example, collectibles is a very cheap niche. So, what are the cheapest niches? Thanks.
Everything depend on Google's rules and regulations. Adsense comes from adwords. if clients bid in cents then how will google pay extra.
As far as I know 'marketing' is a well EPC niche. Actually, the whole business niche has pretty well EPC. The low paying niches are probably the 'entertainment', 'proxy' and a few others.
Arcade's are the cheapest niches. Also, the niches where you are actually selling products in the site doesn't work for adsense. This is because you don't want people to click out of your site, you want them to click further in your site.
each niche has its own payout. all depends on how profitable the keyword is and how much advertisers are willing to bid on it