One such service that I noticed was hire-a-hacker type websites, advertising services like spear-phishing attacks, DDoS attacks etc… as well as just generally offering to ruin the lives of other people by hacking them in a variety of what seemed like rather uncreative ways.
What I wondered though was, are these just dodgy scam websites designed to exploit idiots of the internet who think you can just pay $500USD and destroy someone, or are these actually for real?
If someone advertises themselves as being prepared to ruin someone’s life by hacking their social media or whatever, wouldn’t a person like this just as likely take another persons money and not provide any service at all?
At the B2B end of the market, it is pretty certain there are reliable actors motivated by ordinary interests in maintaining ongoing relationships with good clients.
At the B2C end, there probably reliable retail services but I suspect it is largely a market for lemons. https://saylordotorg.github.io/text_introduction-to-economic... And perhaps a non-trivial number of law enforcement operations as appears to be the case with hitmen.
Like any service, personal recommendations from assholes in your social network are probably your best bet. Good luck.