Ask me how I know.
We took it to a lawyer but he said that it's clearly blackmail but it would be extremely hard to get any kind of judgement against it. We just ignored it and that company eventually folded and disappeared and the website with them, but I'm pretty sure it made hiring somewhat more difficult for a while.
I was interested since I believe we need the sort of quality-control that these review websites offer - the problem is the corruption of the review process that often (always?) takes place, and the crudeness of the review parameters. Google Pagerank (or whatever it is called nowadays) is not a satisfactory quality sifting tool.
If I leave a pie to cool on my windowsill and you take it it's still stealing even if there was no formal agreement or security measures in place to protect the pie.
Adtech is kind of like that. If I give a calendar app access to my contacts I certainly don't expect it to take that information and use it for tracking, targeting, and marketing purposes as well. For me to "give" you that information for free, you'd have to ask for it honestly. And yet Facebook - an ad tech company - has been fighting this kind of consent in the next iOS patch tooth-and-nail.
This is a excellent analogy, thank you.