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All of the top 25 MLMs have been around for 10 years, and most more than 20. There are certainly legitimate startup MLMs, but treat a company that has been around for less than 10 years with caution. Since pyramid schemes are illegal, the top executives generally close their doors as soon as they turn a decent profit. With the internet, it is easy to find a wide number of impartial sources with opinions about companies. Add keywords like 'scam' or 'reputation' or 'review' to get directly to people's opinions. Though pyramid schemes may hire internet marketers to produce false reviews — another illegal practice — you should find positive as well as negative reviews.  The Better Business Bureau (BBB) is a good place to start. It is a nonprofit that processes complaints filed against businesses and resolves questions of illegal or unethical behavior. Another great resource is The Federal Trade Commission website, which has information on companies that have been pursued or fined for illegal business practices. Due to their large pool of self-motivated underlings, MLMs may seem similar to schemes on the surface. However, the MLMs use this system as a substitution for a larger advertising budget. This work is done instead by salespeople on the ground telling others about their product. If the company emphasizes the work of the executives in recruiting new members in their 'downline' over the role the salespeople play, it is probably a pyramid scheme. 'Downline' is a term used by MLMs and pyramid schemes to refer to those who work under you. It can be confusing, since MLMs also give salespeople the opportunity for promotion to a supervisory role. MLMs make their money off sales rather than the contributions of new members. They want to recruit and keep better salespeople, so they compensate them well. Pyramid schemes will glaze over the compensation details of the lower tier to tell you how much money you can make after getting promoted. Push them to give you not only concrete profit margins for salespeople, but actual yearly averages of profit for entry-level workers – not the executives. The MLM strategy is to establish a large population of salespeople to distribute the project and increase their sales force exponentially. Promoters get commission on the sale of the product, as well as income for sales their recruits make. For the pyramid schemes that have, or claim to have, real products, you have to do a little digging to find out if the product is a scam. One way to do this is to find out if you can expect to receive a full refund for unused products. Pyramid schemes often rely on people buying packages of their useless products only to find out that they are unsellable. Then when the people contact the company, they point to the 'no returns' policy in the contract. People move up in pyramid schemes based on how many recruits they sign. MLMs promote people based on their sales numbers or similar performance criteria. If you can promote yourself without an official appointment, it is probably a pyramid scheme.
Find out when the company was founded. Do a web search of the company. Look at the company's structure. Look at the compensation. Find out their refund policy. Find out how you get promoted.