Very good friends of ours have just become IBO’s with Quixtar

My husband and I know all about Quixtar and it’s relations with Amway, as we have done extensive research on Quixtar. They cannot afford to lose the money and time that they will be investing in this company, and they are COMPLETELY convinced and they will be rich VERY SOON. Help. How do we convince them Quixtar is not the way to wealth?