Any business that claims its program is risk-free, works perfectly or never fails is lying. No investment, no business is free of risks. If it promises huge returns on small investments, it's lying. Ask a lot of questions. Ask for detailed information about the company and your earnings potential.
Evasive answers are a sign of a sham.
If a lot of people are leaving the program, it's probably not the lucrative business it claims to be. If most of the products aren't being sold to the public, it's a pyramid scheme. Verify all claims. While it's arguable that MLM is respectable, it's an outright lie that it's taught at Harvard. We never have taught multilevel marketing.