Toe Nail Black Market 

We secretly sell toe nails. Our company makes over 3 million dollars in revenue every month. Basically we are a secret underground black market that specializes in selling toe nail clippings.

Imma buy some toe nails from the toe nail black market. I will make a necklace out of them

Toe Nail Black Market by Kim song dune September 30, 2019

Black Marketing 

The unethical practice enabled by the rise of wiki technologies and communities, of creating and promulgating false and deceptive information, e.g. nonexistent celebrities, events, organizations, ideologies, theories and other phenomena.

He created and promulgated a character who never existed for a Wikipedia entry relating to the iconic TV series, "I Love Lucy," a perfect example of black marketing.

Black Marketing by gatheringman December 30, 2009

blackmarket 

A place to sell children

I sold my newborn on the blackmarket.

blackmarket by steveharveysdaddy January 4, 2021

Blackmarket Studying

When one uses an online resource that consists of a trade network of students who post tests, answers, quizzes, filled in study guides, etc. online for the greater good.

student A: Dude, I'm going to fail that test tomorrow! Our teacher can't even teach!
Student B: You should try blackmarket studying. I'm sure someone has posted the test online somewhere.

Blackmarket Studying by thesolemnstrixisnigh January 24, 2014