This whole argument is built on the premise of the items being black market products, yet I still have trouble understanding what that exactly means here. What

This whole argument is built on the premise of the items being black market products, yet I still have trouble understanding what that exactly means here. What is defined as black market? Where is the line drawn, if there is a line? Marijuana was 100% illegal for nearly a century, it's more legal now, yet the deaths are recent. I am very certain that there is some level of consumer bias toward buying supposed "underground lab" vaping products, having a higher amount of trust in them because marijuana is "legal" now. See where this might get confusing?