Multi-level marketing is a legitimate business strategy, though it is controversial. One problem is pyramid schemes, which use money from new recruits to pay the people at the top, often take advantage of people by pretending to be engaged in legitimate multi-level marketing. You can spot pyramid schemes by their greater focus on recruitment than on product sales.
The legal distinction between MLMs and traditional pyramid schemes has been characterized by many authorities as a legal fiction. Jurisdictions that retain a legal distinction between MLM pyramid businesses versus illegal pyramid schemes retain said distinction on two key distinguishing features: 1) that MLMs always encompass the sale of actual products/services, while traditional illegal pyramid schemes ordinarily do not (though sometimes they do), and 2) that climbing an MLM pyramid is overwhelmingly statistically improbable (especially to its highest participant levels) but not theoretically impossible, whereas climbing a traditional illegal pyramid scheme is both statistically and theoretically impossible.