My friend who has been deep in CPA Affiliate Marketing for the past 1.5 years (also a member on this forum) said that it's not as good as it used to be and people are getting wiped out because of Facebook's recent updates.
Is that true?
Pops were super easy back then because you had mobile apps with great conversion rates, and quality of traffic was also very good, sometimes having publishers with a big Facebook following so you sometimes got Facebook traffic there.
These days, pops are not as easy but they are still a very good source.
When it comes to Facebook it almost always got harder and harder to run BH, and will continue to be the case.
White hat Facebook has been increasing in the past 1.5 years though - either with ecommerce or with digital infoproducts.
I think you should check out the report Matuloo and Vortex put together - https://stmforum.com/whats-working-2018/
It contains input from like 100 people in the industry (affiliates, networks, traffic sources and spy tools). It gives you all the info you need in terms of what verticals and traffic sources are working.