What you want to watch out for are "fast track" programs or pressure to have inventory that requires additional investment. Due to this practice, the law now requires MLM companies to buy back inventory, but that doesn't mean you want to be saddled with debt before you start and truly understand the business. Having a few popular products on hand can be nice, but don't fill your garage with products unless you know for sure, based on your experience in the business, that you can sell them.
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.