John, there are many reliable sources of information on the reasons why your parents should not join Amway. Here are some sources that you can provide to them so they can read it for themselves. One of the many problems with Amway and some other MLM types of recruitment is that it often uses some of the same thought reform/manipulation techniques that cults use - getting people emotionally hyped up in a group atmosphere where the pressure of the group makes them conform to the agenda, promises of success if you do what they tell you and threats of failure if you don't, getting you hooked before you are fully informed about the facts, etc. Here are some online sources of information:

CLICK HERE FOR A PAGE THAT LINKS TO ALL OF THE SITES IN THE FOLLOWING LIST

By the way, my mother got into Amway thinking it would help her make some money when she retired. When my parents died, half of a basement room was filled with her inventory of Amway products. (I tried them, and frankly I thought they were poor quality and overpriced.) My mother had signed me up as one of her down line distributors, and after her death I contacted her customers to see if they wanted to purchase products. EVERY single one of them said they didn't really like the products, and they had only bought them because they felt sorry for my mom. That is all too common a reason people buy the products. They feel like they are obligated to "help" the friend or relative that is trying to make a business of it. All too often, people destroy relationships when they try to recruit the people they know into the business.

CLICK HERE FOR A PAGE THAT LINKS TO ALL OF THE SITES IN THE FOLLOWING LIST

MLM Inquiry and Analysis:

What's Wrong With Multi-Level Marketing? - An insightful and intelligent inquiry into the MLM business proposition.
http://www.whatisgood.com/nwm/ - Dr. Jon Taylor of the Consumer Awareness Institute has posted a most excellent analysis of the similarities between MLM and illegal pyramid schemes.
Multisense: - A set of penetrating questions from an MLM insider, useful no matter which MLM you may be associated with.
Multilevel Marketing: True opportunity or false promises?A conversation with Robert FitzPatrick by Ravi Dykema, Editor - Jan./Feb., 1999 edition of NEXUS, Colorado's Holistic Journal, features an in-depth interview with False Profits co-author, Robert FitzPatrick, on the perils and pitfalls of MLM and why so many in the New Age community fall prey.
The Dark Side of MLMs by Ravi Dykema - A courageous editorial from the publisher/editor of NEXUS, one of the country's leading holisitc journals
The Doctor Will Sell You Now: Medical Doctors Pushing MLM on Patients: The feature article of the July 28, 1999 edition of New Times in Broward/Palm Beach Counties, Florida, exposes the marketing practices of the MLM company, Rexall, which is recruiting medical doctors who in turn recruit their patients. False Profits is referenced and co-author Robert FitzPatrick quoted. Writer is Harris Meyer.
http://wheel.ucdavis.edu/~btcarrol/skeptic/mlm.html - A rational/scientific look at the philosophical issues surrounding the MLM industry.
http://www.quackwatch.com/01QuackeryRelatedTopics/mlm.html Website of Stephen Barrett, M. D. focusing on the questionable claims and sales tactics of MLM companies that market health-related products. Dr. Barrett studied more than 100 MLM companies that market various health products. The site provides examples of dubious products and sales claims from seven well known MLM companies as well as an evaluation of the MLM business model.
http://www.timesunion.com An excellent investigative overview of the MLM industry by business writer, David Orenstein, is available in the August 17, 1997 edition of the Times-Union newspaper in Albany, NY. False Profits co-author, Robert Fitzpatrick, is cited as one authoritative source in the articles. Times Union charges a small fee for downloads.
Equinox Charged as Pyramid Scheme by FTC and Five States FTC Charges Equinox Equinox Article - A journalist examines the Equinox recruitment tactics

Sites that Evaluate, Expose and Report Personal Experiences with Amway, the Largest MLM:

Behind the Smoke and Mirrors - A powerful, compelling new book about the corruption of the Amway distribution system in which upliners make huge profits selling so-called training and motivation materials to unsuspecting downliners. The book is authored by a 14-year Amway veteran who has seen it all and has the courage to tell what she knows. A behind the scenes exposé. Anyone thinking of being an Amway distributor must read this. Also a valuable book for those millions who lost money, time, or direction pursuing the Amway dream machine.
"Little White Lies" - A detailed analysis of the profit opportunity in Amway/Quixtar. This site challenges the very first premise of Amway marketing that Amway distributors "save" money when they buy Amway products. It outlines a financial picture of losses incurred by distributors in the Amway program of each distributor recruiting 6 more who each recruit four and those each recruiting one (6-4-1).
Amway, the Other Side of the Plan - Critical analysis of the Amway sales economics. (mirror site)
Jeff Probandt's "An In-Depth Look At The Amway Business" (This link is to a "mirror" and contains all the same data.)
The MLM Survivors Page - A courageous exposé of deception and myths in the Amway Distribution Channel. Also valuable as a source for current news about Amway lawsuits and other MLM distributor protests.

Government/Regulator Advice and Info:

Profits in Pyramid Schemes? - Information and activities of the Federal Trade Commission relevant to the MLM industry.