I think ACN is among the most likely to catch people, because as you say, it does seem legit. Indeed, their service IS legit – reselling telecommunications. Then you find out the whole thing is one big MLM. Their legality has been (unsuccessfully) challenged by the Australian and Canadian governments. They slip through because they claim that the product is the focus, and the residuals are the main source of income, when in fact the major money is made (by very few) by relentless recruiting.