I'm coming at this from the perspective that recommendation engines are, as far as I can tell, practically a hoax.
The reallity is that once you have a subset of items that matches your behavior recsys are learning to rank problems in the broad sense, and any kind of algorithmic feed (fb, Instagram, news, Twitter) is essentially a recsys.
There is a whole conference around these subjects with very good papers and competitions, look at the different kind of approaches to the recsys18 challenge by Spotify at the ACM site
some type of recommendation engines works really well especially the collaborative filtering types.
Exactly what I was asking about, because I'm not so sure. Furthermore, I think it's a category error to include collaborative filtering here, which is not automated/ML/etc.
Netflix < MovieLens < Criticker < Coollector Movie Database