When I first started out, people used to rave about the KDP free days as a way to build your career as a writer. I don't hear that much anymore, though some people still do get good results from a permafree first-in-series.
I suspect that the competition for free ranks is much heavier than it used to be. Though I haven't looked recently, about 20% of the titles in Smashwords were permafree the last time I looked. And I see some people on BF giving away whole books as reader magnets (though probably older ones in their catalog would be my guess).
If a reader is willing to be flexible, I think that reader could keep busy just on freebies alone.
As to sales relying a lot on marketing, that would be my take as well. The bulk of my sales each month come from AMS ads, except in new release months, when newsletter promos produce more sales (but not anywhere nearly as many as they used to). BookFunnel sales promos also seem to produce quite a few. This month, I don't have a sales promo going, and sales are the lowest they've been all year--except for the one other month when I didn't do a sales promo.
The "good" news is that if I had infinite cash to use for advertising, I could probably do pretty well.
With regard to reviews, I have the same problem with sketchy people offering something that looks suspicious like reviews for sale (even though the wording is often less direct). People who fall for those scams will probably feel Amazon's wrath eventually. I'm also buried in emails trying to sell me various kinds of promos. Interestingly, many of them are almost word for word the same, even though they nominally come from different companies. There's something wrong there, too.
