Around that time, I had seen two fantastic videos done Veritasium on youtube exposing how incredibly sketchy facebook's advertising was (and the situation hasn't improved in the 4 years since):
Video 1:
Video 2:
I tested it out myself and saw similarly spurious results after just $25. Around the same time they also began tweaking their algorithms that murdered growth rates of smaller pages, a science page with over 20K followers I was helping to manage at the time even began seeing declines in activity.
One of the ways facebook pages monetize (generally the main way back then) is by selling merchandise through third parties. However, Facebook began tipping the algorithms against posts containing urls (and good luck getting nonmonetized posts to trend if they have a youtube url) without monetized boosting. Less activity for more money seems to be their monetization model at this point as their active user base continues to decline (and I can't wait to see how poorly it works out for them).
Regardless, hope you enjoy the article, had to break the original essay up into 4 parts since it was just too long to fit in one post.
It's insane that they changed the way they handled everything and ultimately will be the demise of a nice chunk of their income. Not that it really matters to them though....they are loaded. I lost all respect for FB when they pulled this underhanded move and stopped advertising with them. Best thing I did was seek out other outlets!