I'm not sure there is an easily measurable difference, both are generally structured as multi-level distribution, with lower tiers earning money for the people who recruited them.
The difference is that one is genuinely designed as a sustainable business to distribute product, which means that the lowest tier should be able to make money, the other doesn't depend on that for the people at the top who enrich themselves simply by recruiting the lower tiers. If joining necessitates buying a load of stock then it's more likely to be a pyramid scheme.
Avon, Kleeneze, Ann Summers are well known MLM companies. I don't think any of those require any material payments to set up.