There are sites on the darknet that exist to hire contract killers for bitcoin, including joke sites listing just about every famous person along with a bounty, I didn't browse any of them, I got this information from a clearnet blog. Also realistically it depends on the target, someone wouldn't get payed $500K to target an ordinary person.
*There are sites on the darknet that exist to
FTFY
Most (if not all) of those sites are fake, you'll find plenty of articles on the subject matter. IIRC there's only one murder that's actually linked to a hitman that was hired via a hidden service and that one was an amateur that got caught pretty quickly.
Think about it, it's a pretty perfect scam.
You offer murder for hire, but since you're nice you only want 50% up-front. So you take 50% up-front and then... that's it. No one dies, your victim likely is kind of a dick anyway and they sure as hell won't go to the police ¯\_(ツ)_/¯
