What it is
A pyramid scheme dressed up as a job pays you mainly for recruiting other people, not for selling a product, and charges you to join. Since the money comes from new recruits, it eventually collapses and most people lose.
How it reaches you
A recruiter pitches a flexible "business" with big income, is vague about the product, and pushes you to pay for a starter kit and to sign up friends. See is this commission-only sales job a pyramid scheme.
The tell
Income that depends on recruiting a downline, plus a required buy-in, is the pattern. A real job pays you for work or sales and never charges you to start.
What to do
Do not pay to join or buy inventory. Search the company name with "pyramid" and "complaint," and report a scam to the FTC, which explains the difference between legal MLM and illegal pyramids.