How the FTC actually decides, and the test that does not exist. Consumer writing on this subject very often reports a percentage rule: that an MLM is lawful if most of its rewards, or most of its revenue, trace to retail sales to people outside the network. The Commission was asked exactly that and rejected both versions: "Neither is the correct legal standard. There is no percentage-based test to determine whether an MLM is a pyramid scheme. A far more comprehensive analysis is required." So a company quoting a percentage at a recruit is not answering the legal question, and neither is a critic quoting one back.
What the Commission does instead is described in its Business Guidance. It "focuses on how the structure as a whole operates in practice", including marketing representations (statements that encourage recruitment rather than retail sales, and what participants are taught at training and events about how to make money); participant experiences (what participants actually purchased, sold and earned, and what additional expenses they incurred); the compensation plan (in particular whether it requires recruiting in order to reach the more lucrative rewards); and the incentives the structure creates for participants, including incentives to make large or regular purchases in order to stay eligible for rewards. The legal line itself comes from the Commission's Koscot decision and belongs to the pyramid scheme entry.
Inventory loading is the mechanism to look for in a compensation plan. The FTC describes MLMs that set sales quotas as a condition of a compensation rank or bonus and then allow a participant's own purchases to count toward those quotas, saying that such companies "are likely incentivizing inventory loading." It notes that the same pressure exists even without explicit instruction, because the incentive to buy in order to meet the quota is built into the plan. This matters to anyone reading a compensation document, because it identifies the specific clause that turns a sales opportunity into a purchasing obligation: not the price of the product, but the condition attached to eligibility.
Earnings claims, and what a company is and is not obliged to tell you. The FTC's position is that if an MLM meets the definition of a "Business Opportunity" under the Business Opportunity Rule, 16 C.F.R. 437.1, it must give prospective purchasers a Business Opportunity Disclosure Document, and if it or its participants make earnings claims it must also give an earnings claim statement under Section 437.4(a) before signing anyone up. If an MLM is not a Business Opportunity, the Commission's position is that it "is not required to give any information about earnings to potential participants, but any earnings information it does give must be truthful, substantiated, and non-misleading." So the absence of an income disclosure statement is not by itself a violation, and its presence is not by itself reassurance.
On the substance of those statements the Commission is blunt: "Most MLM participants earn little to no money, and, for any MLM for which that is true, the IDS should clearly and conspicuously reflect that." It goes on to name the ways a disclosure can mislead while remaining technically accurate: excluding participants who lost money or earned nothing, discussing only "active" participants while excluding those the company considers inactive, and annualizing income that was never earned. In its complaint against one company the FTC alleged that a single $100 check earned in one pay period out of 24 had been multiplied by 24 to produce an "annual average income". Reading an income disclosure statement therefore means asking who is missing from the denominator before looking at the figures.
A participant is a business owner, and the tax consequences arrive immediately. Income from an MLM is self-employment income from the first dollar, nobody withholds tax from it, and the costs of the activity are only deductible business expenses if the activity is a business rather than a hobby. The mechanics of that sit with self-employment, Schedule C and the independent contractor rules; the point worth making here is that the starter kit, the required monthly purchases, the event tickets and the sample products are all real cash leaving the household before any of it is recovered.