I got thinking about this recently as there has been a right raft of people I see online who go after the extremely low-income demographics (ie, people trying to do 15-20 #nospendays a month etc) and then they suddenly hit them with links for this and that on amazon matched betting or whatever and of course there is zero uptake as you have gone after a community of people with next to no money so they aren't going to gravitate towards your opportunities that cost them money.
I'm hoping to launch a few new websites in 2019 and it really got me thinking about the people I am trying to reach. If i was going to make a blog around say, house cleaning I would litter (ha!) that site with affiliate links of cleaning products etc and I have no doubt give enough time it would work but it really got me thinking about the importance of having a good think about the sort of demographic you are trying to reach in the early days of starting your blog!