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We have tropes for some of the specific subtypes you mention: Serial-Killer Killer and Chained to a Bed. And I guess all of them could fall under the umbrella of Asshole Victim.
I don't think we have a trope covering the general principle in your third paragraph. We do have the Violin Scam as another example of that principle. Shameful Source of Knowledge would be a sister trope.

A criminal pretends to be a drug dealer, prostitute or similar. When a rube becomes interested, the criminal takes him to an isolated location and robs him.
Variations include the child criminal offering sex to lure a pervert, a serial killer making sure his targets are scumbags, and the classic "using handcuffs on a horny guy, then robbing him".
The idea in those cases is the victim understands why they need to be sure nobody's seeing them, and won't tell the cops what happen, for fear of getting himself in trouble.